Find some underwear and fix your outfit

You return to Gwen's wardrobe and start looking for some decent panties to conceal your awkward cameltoe. After all there's no way you could step outside the house while looking like some kind of prostitute. While you're in the middle of looking through various pairs of underwear, the door behind you slowly creeps open and you look back to see Gwen standing there with a look of disbelief.

"Uhmm... it's not what it looks like...?" you reply nervously while putting the pink thong in your hand back into its drawer.

"Who the hell are you? What the hell are you doing here? Why the hell are you touching my panties...?" Okay, this just became a little more difficult to explain. At least she's not calling the cops on you just yet. "Well, this is... not so easy to explain..." - "Then try."

"It's me, John. I woke up this morning to this weird phone call, some woman telling me that I'll be a girl for forty-eight hours, and that I'll be stuck that way if I get pregnant, and when I looked down there were tits on my chest, and I've got a shaved pussy too, and probably all the other equipment on the inside, but I didn't have any clothes, and then I -"

"Whoa, take a breath! John...?" - "Yup. When I was younger, you caught me jerking it to some animated stuff online. That should be proof enough to you that it's me, since there's no way I'd admit that to anyone. Let alone a chick as hot as this," you add while looking back down to point at your feminine curves

"Huh. That's some story. So just two days of avoiding to get pregnant? Well that's... boring. Most girls don't get pregnant for the first twenty or so years of their life, pretty sure you'll manage keeping your legs shut for two days. So why exactly did you decide to touch my panties...?"

You laugh with a faint blush on your cheeks and briefly explain your initial plan to get dressed and leave the house for a couple days. Gwen was understanding but suggested you should stick around, offering to teach you all the basics to get by for a while. She always wanted a sister anyway she confessed, so this was a nice opportunity to have some girl-time.

A couple hours pass and you're like clay in your sister's grip. She fixed your messy hair into a pretty ponytail, painted your fingernails, and taught you how to apply a few simple layers of makeup. You kept on trying to tell her that this is only temporary, but she insisted on sharing her knowledge regardless.

Both of you are surprised when the door downstairs unlocks, and you hear your parents loudly announcing their return. With a rush of panic you look back at Gwen. "What are we going to do now?" Your sister remained calm as she grabbed your hand and the two of you went down to greet them in person, and you prepare to confess the unusual situation. "Welcome back, you're probably wondering who I am, it's me, J-"
"-Jimmy's classmate, Sarah," Gwen interrupted. "She's asked if she can stay here for a couple days and I gave her the permission, if that's okay for you mom, and dad?"

Your parents were still in the process of taking off their jackets and moving the travel bags aside, so your mother simply nodded along. "Yes, certainly, just clean up after yourself," was all she had to say before Gwen took some more creative liberties. "Great! John went camping for a few days and said that Sarah can use his bedroom until he's back."

"Yes sure, whatever, you kids can handle it between yourselves," your mother continued.

Smooth. Made it.

In the evening, Gwen briefly pays you a visit in your already dark room to give you one of her old pajamas, after all it would look weird if you were to start wearing "John's" clothes around your parents considering you are supposed to be merely a classmate and friend of Jimmy. Once you're in the warm comforts of your bed, you allow the day's events to go through your mind again. Regardless of the unexpected changes you went through, things were going pretty well. Your parents had no idea that their precious son was a sexy teen girl. Gwen had taken an odd interest in your female self and seemed a little too happy about having a sister, but fortunately she wouldn't have much longer to obsess over it. One more day, and you're back to what you're meant to be.