Science subjects are quite difficult and need dedication to. There's still a lot of revising you can do, however, if you keep stressing - you'll get nowhere. I know that sounds harsh but it's the truth. Take it as a lesson to start work early and organise yourself next set of exams i.e. don't procrastinate after January exams as an excuse.
To revise, go over the book and your notes, past papers? That's all you can do really, it's as simple as the method:
- Make Notes
- Learn Notes
- Past Papers