Hi there,
As someone who took Maths at AS-Level, your grades seem fine to me.
My advice is definitely not to worry - unlike some subjects, Maths is always about building upon what you already know and expanding your knowledge. Of course, the better understanding you have on your GCSE Maths course, the easier you will find A-Level Maths.
From my experience, because I managed to get an A in Maths at GCSE, the jump to A-Level wasn't as big, but it was still challenging.
As long as you go over what you've learnt, and made sure you understand stuff, then you should be fine (which I did not do enough of).
I'm not sure about A2 Maths, since I dropped it after Year 12, but A2 maths is just again, building upon your AS Maths. Then again A-Level in general is requires effort.
I hoped this helps & good luck!