If you have 90 days left for JEE Main, the single biggest mistake is to start a new topic. Don't. Your job now is to revise, test, and fix — in that order.
Weeks 1–4: Revise every chapter you've already studied in Physics, Chemistry and Maths. Use your own notes first, the textbook only when stuck. One chapter a day, three subjects in parallel.
Weeks 5–8: Full-length PYQs. One paper every 2 days, followed by a detailed analysis session. Maintain a 'mistake book' — every silly mistake goes in there.
Weeks 9–12: Take 2 full mocks a week. Work on exam-temperament — how you sit for 3 hours, when to skip, and how to handle a bad section.
Sleep and nutrition matter more than one extra hour of revision at this stage. Build a routine you can sustain till the exam.
And finally — don't compare timelines with anyone else. Your JEE is a race against the paper, not against your friends.