We get caught

I do my best to sneak out of the room as good as I can, while Martin is busy fucking that poor girl Mey silly. We manage to get as far as to the door, but despite my attempts to open it slowly the creaking sound of the door inevitably gets his attention.
"Where the fuck do you two think you are going?" he asks us, withdrawing his cock from Mey.
"Just to the bathroom." Jen intervenes. Martin looks at her, then at me, then down to my treacherously half-erect monster-cock bulging my pants way too obvious to make that a believable story.
"Yeah sure... you not gonna plan on fucking, do you?" he laughs. Jen blushes.
"No, we really just happen to need to go to the bathroom..." Her voice cracks at the end as she realizes no one is gong to believe that.
"Jen.. from now on you are being honest to me." Martin stares right into her eyes "In fact it's perfectly normal for you to speak even your most deepest fantasy. No secrets." I feel a shiver running down my spine as I realize what he is doing to her. "So tell me: what were you two up to?"
"Just wanted to go to the bathroom and fuck." he admits like it's nothing special "He has such a nice cock."

"So how will the rest learn from that?" Martin returns "We are in sex-ed class after all." He pulls back up his pants and sends Mey and her wobbling porn boobs back to her place. "Come here, just show everyone what you were planning to do." he waves us over. We both hesitate, but eventually Jen walks over.
"You really like big cocks, do you?" he asks with a warm fake smile, and Jen nods.
"Yeah, can't get enough of those." she giggles. Suddenly his eyes focus on me.
"Hey, what's keeping you up?" he asks sharply. Sweat forms on my forehead.
"I-I've... just got that blow-job from M... Cocksucker, and I am not sure if I can go yet again." I stammer. Not my best lie but believable. Martin ponders for a moment then he seems to remember.
"Right... you did that. What was your name again?"
"John." I respond dutifully wondering if he just doesn't care about me at all, or if there is something else in play here.
"Ooooh... right. The big cock freak." he laughs. "Don't worry, I take care of that." I am unsure what he means, but I do feel uncomfortable all of a sudden.
"What..?" I start to ask him, but he interrupts me.
"You don't have any recovery time. You can just go non-stop." he defines. Suddenly the exhaustion is gone from my body, and my dick feels like it hadn't been used in ages. Seconds later I am straining the fabric of my pants, lining out the oversized schlong he gave me to everyone.
"Now come over here." Unsure what else to do I approach them. Jen is already sitting on the desk, ready to 'present' to the class what we are about to do. I suddenly feel a breeze and out of the corner of my eyes see my clothes nicely folded on my desk. Jen and I stand there naked as I was born, and my dick uses that freedom to finally become fully rigid, ending up somewhere with the head of it on my chest. Martin gestures me to start, and having no other option I am once again demonstrating to the class how fucking a girl works. This time her pussy.

"So you love big dicks, do you?" Martin seems to be focused entirely on Jen. He has cursed me already, but as long as his main attention is on screwing up the girls, I might get out of this with only a bigger dick. Carefully I slide the top of my dick into her, making sure I stay within my limits and keep myself from cuming. I just don't want him to block me like last time, or worse.
"Yeah... I could play with them all day long." Jen admits with dreamy eyes, moaning in between.
"So how big is your favorite dick like?" Martin interviews him, and she acts like she's talking about the weather.
"Never can't get big enough..." she moans louder and laughs.
"So... uh..." Martin looks over at me as he tries to remember my name, again. "John... right. So he's a pretty big guy, so he's fucking you good?"
"Yessss...." Jen lets out a moan of deep satisfaction "Just wish I could take all of him."
"Hey John, put it all in." he suddenly orders me.
"I am not sure I fit at my size..." I try to remind him of my like 14 inches of meat.
"I said: all in!" he repeats angrily, and I feel my body flinging forward, **** to push in as far as I can. She winces in pain as I hit her rear end, but I can't stop but to push into her.
"Still wish you could take him completely?" Martin laughs, but Jen just nods in pain "Well then... wish granted!" Suddenly I feel myself moving further in a bit. Suddenly there is no more limit to what she can take. I see a faint outline of my dick appearing on her belly and chest. I have no idea how this works, but the head of my cock must now be somewhere near her collarbone. She makes obscene noises as I am **** to fuck her with my cock literally all inside her now.

"So happy now? Finally having a cock inside you worthy for the slut you are?" Martin laughs at her. I have no idea how he rearranged her internal organs, but I pray it won't do any lasting damage.
"Still wish... he would be... bigger..." she says between her pants an moans. Martin looks over to me, and I can see the confusion in her eyes, but then he looks back at her and decides:
"Well... let's see how much you can take then." Suddenly I feel my cock expanding again, mostly getting longer, but also slightly wider. I have no way of stopping it, nor can I stop fucking her. So the only option left is to internally curse Jen for making him do this to me, while I focus my entire being on not cuming just yet. Which is certainly a challenge if you have your have the entire length of your probably now 20 inch dick being fucked by a rather hot girl. Eventually she starts to cough and I can see the head of my enlarged cock inside her mouth, coming out of her throat. I have a tough time comprehending the fuckery Martin did to that girl, but she's now literally impaled on my gargantuan cock. Martin laughs her ass off, while Jen seems to be stuck between suffocating and having the time of my life, while I pray to god that I somehow find a way to get him to undo this. But then I hear his voice as he speaks to me:
"And what would you like changed about her?" My head races as good as I can in this situation. If I don't answer he might make me speak the truth, and then sooner or later he figures out my little secret. I need to find an answer that satisfies him and matches the show I've been putting up. I look back at Jen, and admittedly with a bit of anger I say: "I wish she had like huge tits. Can't be big enough if you ask me." Martin seems to be satisfied with my answer, and a second later I watch her tits rapidly expand on her chest. It takes her just seconds to go past Mey's size, past basket-balls, past any cup-size I ever heard of, till she sports two massive globes of flesh easily the size of beach-balls, with rock-hard nipples crowning them each about the size of my thumb.
"You like her size?" he asks, and I can't help but to nod. He made me love absurdly big tits earlier, so just staring at them gets my dick even harder than it already was.
"Cum inside her, that bitch needs to be filled up good." he tells me. I am not sure if he did something or if I simply let go, but a second later I am kicked over the edge.

It feels bizarr to cum with a cock this size, especially with the upgrade to my balls he made earlier. I shoot right out of her mouth for a moment till he orders her to swallow. I can see her trying to fight it as she has a tough time even breathing now, but his command makes her. My cock sends the cum through her entire body, then she's **** to send it back the other way. I desperately try to stop early, but his earlier change to empty my balls is still in effect. So poor Jen is **** to gulp down a literal gallon before I finally collapse on her mountains.
"Well done!" Martin laughs. Jen's face is bright red when she finally is able to open her mouth and gasp for air. The next minute is filled with her panting, while Martin is laughing his ass off. Eventually I feel how I can move back again and I immediately pull out my dick carefully. Feeling it sliding through her entire body is as absurd as it is terrifying. I have no explanation how that's even physically possible, but when I finally have it all out I look at a throbbing pole of flesh splitting my vision, and the head of it swaying slightly above my eyes. Thanks to his change to my recovery time I am still rock hard and feel like I could right again. And whenever I look at those bare knockers Jen is now buried under I feel my dick harden fully.
"You look like such a freak." Martin laughs, then ponders for a moment. "I let you keep the size. You like it, don't you?"
"Y-yes." I lie. I don't, but then I don't want him to get angry and do worse to me.
"Now you two can go to the bathroom." he decides. I eye my clothes for a moment before he adds: "Naked." Suddenly Jen and I feel both compelled to walk out of the room as we are.