You need to get out of there and get some answers

You manage, somehow, to tear your thoughts away from your new body and its physical needs and hurry to your room. Your new tits wobble and bounce inside the bra as you move, causing your thoughts to drift right back to them and then even further back to sexy thoughts. You manage to keep it together enough to get dressed in some of the clothes that Katie has left at your place. A tanktop that, with your big tits leaves them spilling out and a good portion of your stomach exposed, and a pair of grey yoga pants that cling so tightly to you that you're worried they might rip if you bend over.

With that, you grab your phone and tuck it into your bra and then duck out of your apartment. It wouldn't do to have either of your roommates find you like this and you're unlikely to get anywhere just hanging around in either case.

It's not until you're on the street that you realize that you jumped into some of Katie's clothes without a second thought. You could have found some of your own stuff that would fit. Sweatpants or basketball shorts or something and a t-shirt. That would serve, right?

Either way, you need to come up with a plan. You could go meet Katie at the restaurant and try to get her to believe that you're you. She could help you try to figure out what's going on. Or you could just... wander? The library could have some info, you guess? Or maybe there's a psychic or wiccan shop that could know something about magic underwear that changes you from a guy into a girl.