They're pretty good! But try and build up some of those C's and D's. You'll feel great on results day if you open your envelope and you've got a row of A's and B's. I wish I had of revised more for my GCSE's, I really regret it! I passed 12 but I didn't like my grades I got.
If you're doing a modular maths course, then you should be able to retake it. I had 4 exams, spread out over 2 years and I had to retake a few.
BTW: Love your username. It's after the band Skindred, right? I saw them last year - AMAZING!