Getting race-fit isn’t like cramming for a test. A sudden slew of hard workouts in the two weeks before a race are a lot more likely to leave you overly fatigued and injured rather than significantly fitter. The important work happens more steadily, less dramatically in the months before an important race.
If you’re heading into a race feeling unprepared, avoid crash training. Revise your goal for the race, run it such that you draw some positives from it and review what went wrong in your build-up so that you can be better prepared the next time.