You only have about 20 more days to go. So there is no time left to start new topics which you had completely left in your class XI and XII (and believe me, I know that you would have deliberately left a few topics as you thought them to be either boring or not that necessary). If you really want to look into some concepts which you think you have forgotten, then look at only those which you had done thoroughly earlier.
This is actually the time to practice and practice. Go through all the previous 3 years question papers of IITJEE (not necessary to go beyond 3 years, as the pattern of JEE changed dramatically after 2007).
Pick up question banks available in any book store near your house and practice. Pick only that book which has solutions (and not just the answers) at the end.
Remember that IITJEE is not a test of your speed or hand writing. It only tests your mental ability and aptitude. So spend lot of time while solving each of these problems that you attempt from the question banks. Do not worry even if you are spending 30 minutes on each of these problems, as you anyway cannot do all the questions from all the chapters. So try a few, but spend most time on each of those only. Look at the solutions only when you just cannot proceed with the questions.
Open your lecture notes from classes you attended in your coaching institute and go through the good problems that your teachers had solved on the board. Go through all the formulae (chapter wise). I’d advise that you only read the theory from your lecture notes only. They will refresh your memory more than any book. Needless to say, you should also finish reading your NCERT books. IITJEE questions are very close to the NCERT now.