Hi uzzy, I see your frustration and understand why you must be bummed out. First of all, I think it's best if you just ignore the numbers and GMAT for a short while (go relax; go do stuff that will make you feel energized and accomplished - such as hiking or whatever it is), then come back with a vengeance and look at GMAT again. Keep in mind that on the GMAT, there are experimental questions for which no one will know where they'll pop up. Also keep in mind that luck plays a crucial role in GMAT (and any other standardized tests). Having said these, it could be that you were just very unlucky and got the experimental questions right, but got the real questions wrong. Other than that, I can't really see how your score would drop that much.
With the Q score that you got, it seems to me that there are certain fundamentals that you may still be confused about. Or simply that you were unlucky on the test and got more of the type of questions that you didn't know how to do, due to the underlying concept. I think it has to do with the fundamentals because even on GMATPreps, your Q scores were 38 and 42, which lead me to believe that you're not understanding most of the basic concepts just yet. Your V32 seems to be in somewhat of a range with your GMATPrep (V38 is a great score on GMATPrep, btw). For verbal, I think you should look at your test and see where your weak points are at. ManhattanGMAT has some very nice books on both math and verbal, with some of its books being the "must-haves" for GMAT preppers (such as SC and Number Properties). You should look into these books and see what they can offer you.
OG is a great source, obviously, and I would wait a bit before going back to
OG for practice to decrease the likelihhood of you remembering what the right answers are. At any rate, the main key is DON'T GIVE UP! Though 520 is not your ideal score, at least you should know that you have great rooms to improve your score right now. I believe that for a person who aims for a 700 would be better of with a lower score than a 680, since a 680 is really just bouncing on the borderline and it could really go either way the next time he/she takes it.
Good luck! Do update us!