Lots of places will ask for maths as part of your offer for CS. I would try and make an effort with it, otherwise you are limiting yourself. Some of it, you'll probably have to get to grips with eventually, so you may as well do it now.
It's not the hardest a-level out there, but if you're not naturally comfortable with maths then it just means you have to put the work and effort in. Don't be afraid to ask for help at all, that's what the tutors are there for. It's by far one of the easiest subjects to do well in, in my opinion, because there's so much past paper content available and simply put: it's all about practice. Have a lesson, learn something, then go and sit and do problems based on it for a while. It's very systematic, so as long as you keep on top of it (allocate yourself a few hours each week to go over what you've done in class).
It will be daunting, but really, just ask for the help and support. Let them know early on that you're struggling (if you are), because you've got the time to sort it out. Try and stay positive, and at the very worst, get a private tutor for a few hours if things are looking really dire. Seriously, trade a birthday present in for it or something, because it will influence where you go with your course and life.