If you go to the intramural sports place inside Blodgett Gym, it's the swim uniform you can buy from there (first uniform is free). It'll make an outfit for you, so just switch to that in the locker room.
I'm having trouble with this. At some point I added a phone case to the outfit, but I've since removed that. In the locker room it says you can't leave because you're not wearing a bottom (for the femme uniform.) A once piece swimsuit and the cap.
Ah yes, that's a confusing bit I keep meaning to sort out. If you're trying to get to a swim meet, you can also join it from the pool, so just go that way after you're in your swimsuit.
