Hi, I'm sorry that I'm just seeing this now. As you've just learned, the forums are not the place to come for emergency help - we aren't checking these folders every day.
If you (or anyone else reading this) have an emergency / last-minute issue, please contact our office directly at 800.576.GMAT (from the US or Canada) or
studentservices@manhattangmat.comI hope that you have no need of my reply (that is, I hope you got the score you wanted and don't need to think about the GMAT any longer!). But here's my answer, just in case.
Some people do have big score drops on test day, yes. Someone is more likely to fall into this category if s/he:
(1) took practice tests under non-official conditions (eg, skipping the essay, skipping IR, taking longer breaks than allowed, pausing the test, etc)
(2) have timing problems (the more serious, the more the score could drop)
(3) have serious anxiety issues (we all feel some anxiety when taking this test, but if someone has physical reactions - racing heart, sweaty palms, difficulty breathing or concentrating - then scores could drop)
As a general rule, MGMAT tests have a standard deviation of 50 points (which means most people score within 50 points on the real test). GMAC (the organization that owns the GMAT) hasn't published a standard deviation specifically for GMATPrep, but the standard deviation of the real test is about 30 points, so GMATPrep is probably either the same or a bit higher.
In other words, you were scoring 600 and wanted a 550, so you were still within the standard deviation range on MGMAT and GMATPrep. (I don't think that Veritas has published a standard deviation - but you can check with them to make sure.)
If you see this, let us know how it went!