I think my cousin always tries to look at me while I change clothes
Why do you think he is looking at you?
Sometimes I just feel like he is looking at me.
If you think he is looking at you changing, you need to call him out or tell someone. He should not be making you uncomfortable like that.
I think I'll be okay. He knows I don't like him looking at me, I'll just ignore it.
This isn't something you should just ignore. I feel the right thing is the tell someone, that way the situation can be resolved. Leaving it unresolved would continue to make you more uncomfortable.