Gym class and self harm scars

So, I have a lot of very noticeable self harm scars covering both of my thighs and my lower right calf. (5 days clean!) I also start changing for gym tomorrow. I'm terrified. They don't have bathrooms next to the locker room or in the locker room, and I don't want to explain to people why I can't change in the locker room like everybody else. I'm freaking out over this. I also have a swimming unit, which I'm even more terrified of.

Help?? I'm freaking out, I can talk to the counselor but I wouldn't know what to say. I feel like I'm going to have an anxiety attack. Thank you!