PERT test for collge!? retaking?

I got 100 in reading, a 78 in writing and a 107 in math... I want to retake it in 30days. BUT if I retake it and I do Worse, will my higher scores remain or will it be replaced with the latest test scores? Also any tips on doing better on this test because I really dont want to take Prep courses since they dont count for anything. this is for palm beach state college.