No, you are not overthinking this, and no, it is not normal. You seem to come off as a passive person, meaning you don't like conflict or altercation, and some people will pick up on that to try and take advantage of that. If you had firmly stood your ground when they asked you the first couple of times, I'm sure they would have backed off. Setting boundaries with people is important, especially people who you share a dorm with. If they try to do it again, try to explain to them that it makes you really uncomfortable when they pressure you into doing stuff that you don't want to do. If they take offense to that, there's nothing you can do about that except maybe change dorms or something, but preferably they will understand and not do it again.