I am not sure what you mean by" not learnt anything" actually you have not studied or is it your anxiety which makes you say that you have not learnt anything. Well, in 20 days, you will need to cover a lot of content which means that all kinds of distraction like computer, mobile, tv, friends will take a back seat and you will focus your attention on your studies, small periods of relaxation, eating and sleeping. You will need to organise your time in such a manner that you are able to give ample time to important portions to study. If you want to leave out unimportant portions, then do so. Walking and loudly repeating what you have learnt helps to retain for longer. Make points and elaborate in your mind. Use a highlighter to mark out important portions. Use mnemonics and abbreviations like vibgyor to help retain portions faster. Using all senses to learn portion helps immensely. You can attach a mental image, smell, music or color to various things to access it faster while reproducing content in the exams. Reduce junk foood to minimum and eat only brain healthy food to increase focus, retention and reproduction. Exercise everyday to improve blood circulation and mental alertness.