You figure you don't have much to lose at this point. If you want to take care of Megan, you can later whenever you want. For now though, you've got nothing to hide. Megan won't stop banging, so you slide the gun under the bed and open the door. Sure, you're buck naked, but what do you care? Megan takes one look at you and her jaw drops: not just from surprise at seeing a naked chick in your room, but that you're so amazingly hot. Megan's not bad yourself, but your new body puts hers to shame.
"Who... who are you?" she says. "Oh, it's still me," you reply. "I figured out a way to change my body, and I wanted to see what it was like to be a woman."
Megan just stares at you, still slack-jawed, for what feels like forever. Sure, you expected her not to believe this pretty outlandish story, but she's taking so long to respond that you wonder if she even heard you.
So you break the silence. "Look, Megan, it's still me. You steal my peanut butter, you leave late for math on Tuesdays and Thursdays because you hate it, and you think it's okay to run the blender at 2:30 in the morning. I've just changed my body. What do you think?" You do a little twirl in hopes that your looks-obsessed roommate will relate to that.
And it works. "That's ... that's amazing," she says. "Is it different? I mean, does it feel different being a girl than being a guy?"
"Yeah, I think so," you say. "You know, a lot of it is just having a different center of gravity. I wanted to see what it felt like to come as a girl, but I didn't get a chance yet."
"You want to have sex as a girl?" asks Megan. She's forming sentences all right, but she still looks completely confused. You can't really blame her though. In fact, you're kind of surprised she can handle it at all.
"Yeah I want to have sex as a girl," you reply. "I've never been pleasured this way before. I want to feel how the mechanics work from this perspective."
Megan smiles, the first change of expression she's had in a while. "I can help you with that," she says.