Retaking A levels at uni?

So i got my results back yesterday and I got a AAC, with a C in maths. I got into my first choice university for computer science, but was 9 UMS off a B in maths. I got an E in mechanics paper 1, and i know i'm easily capable of at least a C in M1 to bring me up to a B in A level maths. So i have a couple of questions.

Would it be possible to retake it during uni to bring it up a B, how would i go about it, and would it be worth doing so?

Thanks