Will 3 years at college impact chances of getting into university?

I don't really feel confident about my upcoming as-level exams and in order to get into the university course that i'd like, i'd need atleast AAB and at the moment i'm looking at CBA/BBA. I'm thinking about retaking some subjects again next year but if I do, i'll be at college 3 years. Would going to college 3 years look bad against someone who went for 2 years? I know I'd have more subject knowledge but I guess a question would be why I wasn't good enough to just do 2 years a-level study?