May be you are stressing too much. 8 hours of hardwork is not a joke. If you are stressed out, the brain will get tired easily and so cannot remember things. It might affect your performance and your preparation. Once you relax, you will slowly be able to concentrate more and be able to remember the topics and concepts more. Then it becomes easy for you to score good. Take small breaks in between for your preparation. Also write formulae on the Post its on Flash cards and stick them wherever you can see them. When you re revising a chapter, make a note of all the important topics or formula and keep it as a post it. And immediately try answering questions on that topic. Also there is no better way to excel than to practise as many mock tests as possible. Stop worrying because that will only add pressure.