Don't give up, but do try to evaluate your preparation. One thing which jumps out at me, is that you may have framed your expectations by your practice tests. The reason I think that's not so good, is that you lock into a mindset that way, and also forget that your study conditions are not going to be very much like the test conditions. What I mean is, back when I was an undergrad, I found my grades were not all that good, and a friend warned me that I was aiming too low and letting myself coast. That is, if I expected to get a 'B' and would be satisfied by a 'B', then if I slipped I could get a 'C' or worse. The idea is to aim for 100%, reminding yourself how much work you will have to do to get that result. Almost nobody fools themselves into thinking it's easy to get an '800' on the GMAT, so if you tell yourself that's what you are aiming for, you know you will have to work.
Next, pay less attention to your practice score results and more to your
error log. Track what kinds of questions you are getting wrong, because sure as shooting those kinds of questions will be plentiful and stress you out on the real deal. Remember that in a practice test, it's easy to relax when you see questions you can't answer, because you know you can look them up later for study, but when they happen in the real test, they can destroy your confidence and mess with your concentration. Also, you want to avoid getting lazy (forgive me for that word) in the test. We all do that at time - we are getting a little tired or distracted, and so we are not sure about the answer to a question, but one "looks right" and we choose it without really thinking through. You'd be amazed how many people make that mistake, especially since the test is designed to offer wrong answers which
look good.
I took all kinds of practice tests, and got scores anywhere from 550 to 760. While it's true that my scores came up as I studied, the last practice test I took was at Rice University under real-test conditions, and I only got a 610 on it. That told me that my practice conditions were not realistic, and so I buckled down on my
error log, worked on Geometry and Data Sufficiency and Sentence Correction, which were my personal potholes, and worked a 730 on the real deal March 14.
Do you know when you will retake the test? This will help you plan a schedule for your study and error-log review.
Good luck.