Confused- AS level resits for A grade subjects

Ok, I got AABC (dropping the C subject anyway)

But even in my A grade subjects i did poorly in one unit but great in the other, so should I resit one?
For example:
100/100 (A) + 61/100 (C)= A
100/100 (A) + 74/100 (B) = A
149/200 = B (but got A in one unit and C in the other)

My teacher wants me to redo the one poor unit in each subject whilst doing one A2 exam early in January :s-smilie:

But, if I want to be considered for UCL/Cambridge/ Oxford, would you suggest re-sitting or simply trying harder at A2? Because I've heard that they don't accept resits.

I'm aiming for AAA or A*AA- is it still possible to achieve that with my current grades? Do the top unis look at individual module marks?

Thank you for your help.