Hi, I just felt like offering my own opinion on this matter... I took AS Maths, and am about to take the AS exam in October. I find it really easy, basically because it was almost all a repetition of my secondary school maths.
But then again, I love Maths, I don't know about you...
And it might be a little difficult for you to learn Maths without a teacher, and since you like computing so much, I suggest that you do what you like best, and enjoy it!