People on this forum generally believe, that GMATPrep is a pretty good predictor of the real GMAT score. It means that if you did well on GMATPrep, chances are that you already have all the skills and knowledge necessary to score 600+ on real tests.
It looks to me like you were studying very diligently before the tests. If I were you, I would take long break form studying, and let my brain rest. I took long break in the middle of my GMAT preparations and my GMATPrep score went up 100 pts.
And I would make sure not to take actual test in the last moment. You do not need additional stress on the test day. Do not try to get 600+ so hard as well. Just prepare well and do your very best answering each question. Sooner or later you will get the score you need, because there is no limitation on the number of times you can take the test

. And after each time you will benefit from additional real test experience.
And try to do better on your prep tests. Chances are you will always do worse on the actual test, because you are one of the people (like me) who do not handle well stress involved in taking tests. So if 100 pts is the stress factor you have to deduct from your practice test score in order to arrive at the actual GMAT score on the test day, save your money and do not schedule next test until you get 700+ on your practice test.
Best luck!