I got an A* at GCSE maths, then went to A level and i'm pretty lazy... (didn't revise for any GCSE)
When we started Core 1 a couple of weeks in we had a little test on basic algebra, I got an E....
I found maths really hard to start with, but it does get easier!
i've completed AS now and waiting for the results, but i'm pretty sure i got an A. Just make sure you work hard because if you don't it will just all show when you read the results in august, you can't really fake being good at A level maths you need to actually try.