Username checks out (sorry, couldn't resist as it said Sonic, gotta lose fast).
This is only Year 10, you can turn your grades the right way up. You should be revising for an hour minimum daily.
Revision methods are very important. Maths, Physics and Chemistry requires practice, so you should attempt, mark and try to understand your mistakes in as many past papers as possible. Biology - Use flash cards or read mind-maps, memory is a key point here.
Finding your best method of revision takes a bit of experimenting and time.
I was the worst in Science and Maths in my sets. Nothing has changed, still the worst in Year 13. Don't let being the worst put you down, if you're the worst in the room, you're in the right room, remember this.