Wow, you need to calm down. At the mo, I've got lots of B's, one A and one C (I'm in Year 10 too). At first I was rather disappointed with my grades, but I realised that I have another year to improve them (including a nice fat summer holiday) and I could easily go up a grade or two if I try hard enough.
For example, I did mock papers in Maths in class, and I kept getting C's. I was going to Saturday school at the time, but it wasn't really sinking in too well. So I revised and brushed up on my maths for a couple of days, and don't you know I got a B in the next paper. After a few days of scruffy, haphazard revision!
You should feel very lucky that you've realised what to do this early! You have another year ahead of you, and it's really not hard at all to get decent grades at GCSE. You just need to put in enough work.