With three days left, do not rebuild your entire case skill set. Focus on the math errors that are actually recurring and keep casing sharp with a small number of complete cases.

Spend one focused block each day on arithmetic, percentages, ratios, and setup. Then use one full case or targeted math-heavy case to apply the skill under interview conditions.

The day before the interview, reduce volume. You want speed and confidence, not exhaustion from cramming. If useful, this guide on case interview mental math gives more detail.

3 days out I would NOT try to become a math wizard. fix repeat mistakes + keep casing.