All you need to know is that success in GCSE is relative to the amount of hours you put in
With revision, a lot is possible. People forget that yes while academia is partially intelligence, a great deal of it is putting the effort in and knuckling down remberimg content and practising how to answer the questions. I'd say you are capable of at least all C's and B's but there's no reason why you couldn't get all B's or even a few A's if you really try. There's 6 weeks left now, so you should get a wiggle on but I believe anything is possible if you actually work hard!