I want you to do the following workouts leading up to your race:
2x(3x300m), 3 minutes between reps, 10 minutes between sets. Go for 45,42,39 each set. Rep one should feel super smooth, rep two should feel hard but in control, and rep three should ruin your day. Rinse and repeat.
3x400m, aim for 55-56 on each rep. Take as much time as you need between them. We are talking 10 minutes between reps here. This is trying to simulate the first lap of your race.
50m, 100m, 150m, 200m, 250m, 300m. Every rep at 95-100% effort, 4-5 minutes between reps.
EDIT: don’t do all three of these in the span of 1 week. This should be a 2 week workout cycle with 2 recovery days between each and a lighter tempo/threshold workout thrown in there.