I don't think you are horrible.

I'm really sorry you are feeling so low. I can see how upset you are about hitting your mother.

It's no joke being a teenager, even in a normal house.
It's no joke living with a parent who can't cope.
I think most people have defied their parents in one way or another at some point in their lives.

So: you shouldn't have hit your mother, but one incident doesn't make a monster.

I can understand your fear of "becoming your mother". I'd be scared too.
But here's the difference: you have sought help, you are being helped, and you will get better.

And one day you will be a great mother.