Schedule a re-test. You have to wait six months between each exam, so you will have plenty of time to prepare.
Get a private tutor if you can. Private tutors can be expensive, but they can also be the best way to get the individually focused help that you need. They can work with you through each practice test and answer any questions that you have on the spot.
Take practice tests online. There are many websites that offer study tips and practice tests to help you prepare for the exam. Though not as thorough as a private tutor, these sites provide free help and information whenever you need it.
Make sure you get plenty of study time. You aren't going to get a better score, if you don't put forth the effort. Focus on the areas where you performed the weakest and review each topic with your tutor as many times as you need to.
Take several practice tests "on the clock" until you begin getting perfect scores. By timing yourself and treating the practices tests as the real thing, you will have a better idea of how you will perform on the actual test day.
Eat a good breakfast, the morning of the exam, and get plenty of rest the night before. You may not think that this is an important step, but these two things will boost your concentration and stamina.
Take the test, do your best and get a better score.