Behind the back piece there looks like theres another locker room. But that doesn't make sense, This Wall, is against the outside of the building, it couldn't physically be there, besides, this is the only Locker room, The Women's is behind you.
You try and stick your head through but can't quite get far enough in, so against your better judgement you slowly climb into the locker, its pretty tight, bu you manage to fit, you stick your head out the other end and see an empty locker room, that looks identical to the one, you're in, except its a mirror image.
You climb the rest of the way through and stand up, straightening your clothes, But somethings odd, your white tank top has shrunk considerably, not its just hugging your tits, which is another thing, You've got tits.
You run to the Mirror and see yourself, a girl, with brunette hair in a ponytail, in a sports bra and yoga pants.
Alarmed and confused, you do the only logical thing, climb back through he locker.
Luckily, back on the other side, you're a guy again, in your own clothes in your own body.
Now that your safely a guy again, curiousity takes over, especially since you can clearly go back and forth, why not check out that side a bit more.
You grab your stuff, including, your phone wallet keys and clothes, and check to make sure nobody's around, and quickly slide through to the other side.
You're back to being a girl, even th stuff you brought over has changed, you're now carrying a purse, a skirt and blouse, along with some underwear, panties and a bra, and even a pair of heels.
You marvel at all this, there must be some sort of portal or something right there.
Curious to see if anything else has changed, you replace th false backboard and close the locker, leaving your clothes in a pile for now, You head back out into the gym, finding it looks identical, even the people are the same, the two heavyset guys walking on the treadmill are the same and the TV's are all on the same Channel, it seems you are the only thing that's changed.
You've got several options it seems