Failing

I'm 17F, last year of school before going to uni and I feel hopeless. Chose A level pure maths as my second a level, even though intermediate would of sufficed and the subject is breaking me.

Picked it cause i thought it would be "cool", but I've been holding myself back with it. It's a lot of stuff and I can't get myself to study and focus on it, it's pathetic. Had my school test today, prob failed it, was an easy paper, but thinking about it made me stuck for weeks. How am I gonna explain that to my parents, and my teachers?

Did this for my other subject too(psy, philo, English), but did farely good in them(b, b, c) because they're mostly just reading. I hate that I keep falling to the same thing. It just makes me wonder about how I'm gonna survive uni if I can't even do this.