Hi Joe2244,
Your GMATPrep scores are 100 points or higher than your actual GMAT scores. That is too large of a discrepancy. I am assuming that the GMATPrep tests that you took were at one sitting, that would definitely be more representative. Also, taking a test home is different than the test center, the energy is far more intimidating at the test center. That is just the way it is and every one of us has to deal with. That is one reason I recommend taking the practice tests in an unfamiliar place, such a public library.
In any case, to me it seems the pressure and stress of the real exam is getting to you. This is fairly common and the only way to get over is to add practice under time and pressure. Of course, you should strengthen your core concepts in areas you are weak, because that also adds to the confidence.
I would say start with easier sets of questions, and then warm up to a format that is closer to the real exam. This is what I do with my students. For example, you could use these old GMAT paper tests for getting in the groove:
10-full-length-gmat-pen-paper-tests-137463.html#p1113860 . Only use the first six tests, try a few sections and do them in the time listed at the top each section. The questions on average are easier, but you have less time.
After these sets, move on the GMATPrep Question Pack 1 and create sets questions for quant and verbal and do them in 75 minutes.
How best to use Question Pack 1. These would be closer to the exam, not perfect because you won't get a score but will subject you to the stress and pressure of the exam.
After this you can take the computer adaptive tests from Exam Pack 1, to test where you stand. Of course, as you go through practicing all this make sure you review your mistakes and learn from them.
Cheers,
Dabral