How do I stay confident despite things going on?

That's really hard. It sounds like your mom is an amazing woman for letting you go follow your dreams. I would say that everything you do should be for her. Fulfill your dreams for her, so she can see that you are happy and successful. Let her live through you. She wants better for you, and the best thing you can do is go out and get that "better" for yourself. Who knows your own drive and ambition just might inspire your mom and change her for the better.

I feel like it is okay to be selfish once in awhile, you don't want to neglect yourself. Just look in the mirror every morning and night and compliment yourself. Instead of picking at the flaws, tell yourself, "Gee, I really like how I did my hair today." Start spoiling yourself. Start going to bed a little early and waking up early and doing your hair and makeup and before you start saying "I don't want to have to look good for anyone." Exactly, don't. Look good for yourself. Ask yourself, "Do I look good in my opinion. Do I feel happy?" At this point you will notice your mood a lot happier, your grades more improved. Have your mother come to you and visit you, show her how happy you are. It will effect her confidence and stand up to your father.

if u are selfish a bit now you will find your dreams and that will make u start earning money so you could move out u and your mom so this way she would have a push to leave him , cuz really she should never stay with him and he abuse her so u should work hard and try to study harder so u could be a step ahead to help her by helping your self