A hundred days sounds like a lot until you subtract bank holidays, half-terms, and the two weeks before the exam when nothing new should enter your head. The usable core is about seventy real study afternoons.
Start with a diagnostic. Sit a full past paper for every subject under exam conditions, mark it honestly, and note which chapters cost you the most points. Confidence is the least reliable signal you have.
Divide the days into three blocks. The first sixty are for repair — the specific chapters your diagnostic flagged, in the order that closes the biggest point gaps first.
The next twenty days are for pattern practice: full sections under time, then targeted drills on the question shapes that ate your minutes. This is when the error log earns its keep.
The final two weeks are taper. No new material. Old mock papers re-marked. Sleep hits nine hours a night. Arrive rested, not sprinting.