They usually do what's called ''fast track'' which is one year (start sept to take the exams in june) instead of the 2 years which it would be done in school.

Surely you know whether or not you got a maths gcse?.did you not keep the certificates lol?

You'd probably want a science, english (language I'd pick over literature..less reading, more written work of your own)..and maths? then something else to fill in the gaps..like geography and history if you want 5? or IT if you are any good with pc's..?