I wouldn't recommend doing it with a C. One of my friends who did A-Level Maths dropped out half way through the year and he got C at GCSE. Does your college offer Core Maths? It would be a great idea to take that up if you wanted to study a Mathematical subject. It also depends on what university you want to go to, some university will accept you without maths as you have computer science, and with you taking physics that will help alot.