Hi mubrang,
The Unofficial Score that Test Takers receive is almost always the same as the Official Score (once the results are certified). In some rare circumstances, the score might vary by 10 points, but you should not expect that to happen.
GMAC has publicly stated that the Official Score that you earn on Test Day is within +/- 30 points of actual ability. As such, you could have very easily scored 500+ on the Official GMAT, but you made a silly mistake or two on some 'gettable' questions - and that cost you the points that would earned you a score at that level. Thankfully, you can retest in 16 days. However, you should not 'rush in' to retest without analyzing how you studied for this initial attempt.
1) What is your exact goal score?
2) How do you know that a 500 would 'be enough' for the Schools that you're interested in? Does that score 'guarantee' you admittance (and how do you know that for sure?)?
3) What application deadlines are you facing?
GMAT assassins aren't born, they're made,
Rich