You pick the spandex.

Well, out of all of them, the spandex isn't so bad. At least it will stretch to accomodate you. "I'll take the spandex," you inform her. She hands you the pink and purple pieces.
As you step into them, she begins, "So you are going to be an aerobics instructor. I am going to be a schoolgirl who needs more exercise. You need to get me to work out. I'll go slip into these." She walks out and closes the door. You examine yourself in a mirror. You are in one of those leotards with the crotch that pulls up over the bottoms. You were right that it fits you perfectly, stretching over your cock and balls, but doing nothing to hide them.
You hear a knock on the door, and hear a very timid voice say, " I'm Sally, here for the workout." She is changing her voice and everything. She must really be into this. She lets herself in, and you see a very lewd sight.
She is wearing a schoolgirl uniform, with her tits literally spilling out of the top of her shirt, which has the top four buttons undone. You see that she didnt even try to zipper the small jacket, and her jutting cans keep it wide open. The bottom of her shirt rides so high the bottom of her tits stick out of the bottom slightly. Her skirt does little to hide her huge bubble butt; the bottoms of her ass cheeks stick out of the bottom of her skirt. What is hidden even less are the cantelope-sized balls hanging down stretching her pantyhose down to her lower thigh. Her 15+" cock bulges out in the front, tenting her skirt but hidden.
"Howdy Sally. I am instructor Dick." You gesture for her to move to a position near you. "You look very lovely today, Sally, if you don't mind me saying."
She fakes being disgusted at the comment. "Let's just do this so you can write down I did what I had to."
You nod, "Ok then. Bend and touch your toes." You watch as she bends over, and her skirt rides all the way up her luscious butt. She then pulls herself upright, and pulls down the skirt to cover as much as possible. "Now do jumping jacks. Twenty of them."
She looks at you with disdain, "Jumping jacks in this? Get real, perv."
You raise your voice, "Either do it, or leave and fail gym class. You can fulfill you requirements here, or do them with the rest of your class." She seems intimidated, and begins as you ordered. You are rather enjoying roleplaying. You enjoy the sights as she jumps up and down. Her skirt flies up to her waist each time, revealing a large bulge in her girly pink silk panties. Her balls are hanging outside of it however, resting in her pantyhose. They bounce up and down as she does. Her tits slip around inside the tight white dress shirt. After twenty are finished, she is panting and sweating. You aren't sure if she is faking, but it might be possible since she is hauling around a few heavy pieces of machinery.
"I'm done for today, perv. Write me off," she sneers.
"No, I don't think so. That mouth of yours is going to cost you. Do a split." She looks shocked, and is about to say something, but thinks better of it as you go to rip up her contract. "Oh, and no hands. Keep them on your head. That will make it hard to balance, and stop you from making it easier to lower yourself." She goes down slowly, her hands on the top of her head. You watch as her skirt rides up as she makes it most of the way down. She stops as her balls begin resting on the floor and you hear a tearing sound. "Keep going, that is not going to excuse you," you command as you see her pantyhose tearing at her crack. Her panties are wedged tightly between her cheeks.
"I can't," she whines. "My clothes are torn and my balls hurt as I lower myself into the split. Can't I just stop?" You are about to tell her to stop, when you decide to do something else.
"Here, I'll be nice, and help you with your split." You pull down your spandex pants in the back and slide the crotch to the side. You bend over her face, and pull out the plug that is holding back a lot of cum. Cum gushes out over her face, soaking the front of her shirt.
"What the fuck!" she exclaims.
"You can expect something else if you don't finish this." She manages to thrust her crotch a bit, getting her balls swinging enough so they rest in front of her. She doesn't get all the way down. You take a crack at her ass next. Her crack is very tight as she is on her way to the split. It is deeper too. You find the plug and pull it out. Cum soon moistens her leg as it runs down them, and seeps into the fabric of her silk panties, soaking toward the front. She starts fussing again, until you dive between her cheeks and spread them with your hands. You shove your cock inside of her hole. She gets the hint, and finally completes the split.
"Ok, I'm done now, take it out!" she complains. "I'm already soaked through with cum!" You pull her hands behind her back so she has to stay in a split as you fuck her jiggly ass. Instead of cumming in her ass, which is already sticky, you pull out and bust in her hair. She shrieks.
"Now you are done." You wipe your sticky hands on the back of her shirt. She is sitting there in a split, looking defeated. Her hard cock betrays her though. It juts out of the top of her pink panties. "Well, maybe I was too hard on you today. Here, I'll help you with that."
Since she is in a split and can't move, you decide to just lower yourself onto her pole which is sticking out away from her at a slight angle. You face her, and quickly lower yourself until the head presses against your hole. You begin your decent again after only a split second. It takes a very short time to sheath her inside of you, since you let your full weight fall onto it. You feel your spread ass resting on the huge sac. You ride her, slowly at first but it gets faster as she grasps your ass to help you rise each time. Then she cums without warning inside of you. You both push her as deep inside as possible.
After it stops flowing...