Focus on short term memory techniques in your revision, and in future you should start weeks if not months before. Depends on how good you are and whether you study well. I have a bad study technique so have to start earlier, like months in advance; yet the subjects I'm best at need only a few weeks revision. At GCSE admittedly you don't need months and months, but 2 days is much too little time depending on how good you are at the subject.