I need to tell someone this: I don't want my stepdad to be in the same room with me while I'm changing.
Does your stepdad stay in the same room when you change often?
Yes, I'm really uncomfortable with him being in the same room with me while changing. He has been staring at my body for a while.
I can see where that would make you uncomfortable. You should talk to him about this if you're comfortable doing so. If not I'd suggest talking to your mother about the fact that he does this.
I don't want to talk to anyone. I just want to get some clothes that will help me avoid him being in the same room with me while I'm changing.
Until you get this sorted out, I suggest you change clothes in a private place with a lock on the door. Him staring at you is not right and you need to tell someone about this.