I don't think your problem is weird. It sounds like you're afraid going over time means you're like your mother and that your T will therefore see you the way you see your mother and have similar feelings towards you. I think you need to talk with your T about whether he feels able to set boundaries and not feel put upon, as you need to find a way of seeing that you're not being like your mother. Maybe agree that he will tell you if he wants you to go, or something.

I'm the opposite to you. I didn't get enough/any attention from my mother and as a result I am pathetically grateful if we go over by even a minute.