Hello!
I am a bit biased as I've always enjoyed maths a lot. I got and A* in GCSE and have had no trouble with the AS. It is actually the AS I've enjoyed the most as you only need to practice a lot. I think that if you got an A at GCSE you should go for it, as it means that you are pretty good at it, and it may be that you regret not taking it in the future as universities really take it into account.
I hope this has helped.