Hi student ,

You want to appear JEE mains 2021 for next year . As you know and you have also mentioned that you are running a short of time . I hope you are aware of the syllabus of JEE . If you are aware just start it with the easy topics you can go too which you feel easy in 12th . It doesn't matter to score in all three subjects of paper 1 just make any two subject best and get passed in third one you can still get IIT . You have to start studying atleast a 8-9 hr a day for JEE from now . But start it by doing 2hrs a day and just add 20 mins extra every day . It will be easy for you to develop habit . Go online and search for the lessons which can be done easily prepare your timetable with an aim to complete atleast one chapter in a day or two . In two months you can be on top but you can still crack it just make a proper plan and focus on it   .

Best of luck!!!