You look into Mina's eyes. "Wow, I guess that wasn't very smart."
"Yeah," he admitted. "But it felt so good! Now I know why you didn't pull out of me the first time either."
The teacher was standing nearby and smirked. "I see you're all coming to the correct conclusion." You wanted to listen closer, but Mina was still slowly moving his softening cock around inside your new vagina and it was very distracting. He grinned at you as you bit your lip, trying to keep silent.
You couldn't believe how attracted you were to this boy. It made no sense! You liked girls! But now that you were one, looking into Mina's strong, brown eyes made a direct connection to your pussy which clenched his cock in response.
The teacher continued. "But that's not enough. Everyone in this room made the same mistake. Half of you ejaculated inside a girl without protection, and then the other half of you did the exact same thing. We're going to have to go further to make sure this lesson sticks."
And with that, the teacher pushed another button on his device and the room flashed once again. You saw Mina shiver and felt his weight lift off of your body and his cock withdraw from your dripping pussy. At first you thought he was standing up, but after a moment you realized his full weight was still pushing down on you. He wasn't standing up. He was losing weight!
And he wasn't pulling his hips back. Rather, his cock was shrinking. You looked at his firm chest and watched as it melted back into two soft boobs, much like your own. You both sat up as your eyes remind locked on Mina's changing body. His legs slimmed and his... well, her now... her hips widened back to their familiar, feminine shape. You watched with fascination as her cock gently slipped back down into its former role as a tiny button nestled inside Mina's flowering labia.
You felt a sense of disappointment. You'd been very attracted to Mina's male body and her female one was not nearly as interesting to you. But wait... why was that? You remember liking it very much at the start of class. Shouldn't you like girls again now that you've changed back?
Your question was answered as you looked down at your own body. You were still entirely female! A quick glance around the room confirmed that all of the temporary boys had returned to their female bodies, but every single former male hadn't changed at all! What was once a mixed-sex group was now a gym full of confused young women.
The sight also confirmed your suspicion that you were still a straight girl. Not a single one of these naked ladies turned you on in the least. It was very weird to remember liking girls this morning but to have an entirely different opinion on the matter now!
As if to confirm your new status, you felt Mina's cum start to slip out of your little slot, dripping down and pooling under your buttcheeks. You shifted your weight, uncomfortable at the stark reminder of your new body. You shivered at this thought and felt your boobs jiggle because of it. There was no escaping the truth of your full female-ness.
The teacher raised his hands to settle down the room's chatter. "As you can see, you're all in the same boat now. Every single one of you just had unprotected sex as a male and as a female. As such, you're all going to face the same consequences. Every young woman in this room is now pregnant and you will be crying your babies to full term."
The room was filled with a series of gasps and shrieks. You looked down at your smooth stomach and gently touched it. As a boy you'd never even considered the possibility of a life growing inside of you. And now in the span of 30 minutes it had gone from being impossible to being possible to being a certainty!
"Now, don't worry about your own lives," said the teacher. "Once you give birth we will arrange adoptions for all of your babies, return the males to their original bodies and, finally, we will de-age you all 1 year so you can repeat this grade and not be behind in your studies."
You were barely even listening anymore. You looked at Mina for some sort of comfort and found that she was also looking at her stomach with a distressed look on her face. Your life had been completely upended and you didn't know what to do next.