By the time ninety days remain, learning new material has stopped being the priority. What decides the score from here is retention, accuracy and stamina — in that order.
Weeks 1 to 4: consolidate, do not restart
Resist the urge to begin the syllabus again from the first chapter. Instead, list every chapter across all three subjects and mark each one strong, shaky or weak. Spend this month almost entirely on the shaky ones. The weak chapters are usually low-weightage and expensive to fix; the strong ones need maintenance, not attention.
Weeks 5 to 8: full-length tests, twice a week
Take the paper at the actual exam time, in one sitting, with no breaks and no phone. The purpose is not the score. The purpose is discovering that your accuracy collapses in the third hour, or that you routinely spend eleven minutes on a question worth four marks — and then doing something about it.
Every test must be followed by an analysis session the same day. Categorise each wrong answer as: did not know it, knew it but misread, knew it but calculated wrong, or ran out of time. Those four categories need four completely different fixes.
Weeks 9 to 12: NCERT and your error log
In the final month, Biology should be pure NCERT revision — a large share of the paper is drawn directly from those lines. Physics and Chemistry should come almost entirely from your own error log. A question you have already got wrong once is worth ten fresh questions, because it targets a gap you have proven you have.
What to stop doing
Stop collecting new material; nothing acquired in the last month will be retained under pressure. Stop comparing test scores with other students, which measures anxiety rather than progress. And stop studying past midnight — the exam is in the afternoon, and your concentration should be trained for that window.