Work on chemistry and biology. Maths and physics are logical subjects, so if you're as smart as you say you are, focus on chemistry and biology because their mark schemes can be super dodgy whereas the mark schemes of maths and physics are straightforward. This is from an AS Level student who should have started revising so much earlier (earlier than the first week of April). Basically, we're in the same boat and that makes two of us. Keep calm and study hard! XD