1. Do you have identifiable weak areas?
If yes, I would recommend re-taking the GMAT! I have had students show substantial improvement in their test scores by working with me on their weak areas. The ones who don't have specific weak areas that can be identified tend to show a smaller improvement but they too tend to score higher when retaking with help.
2. Did you score less than the average of your GMAC full-length practice tests?
That means you've underperformed on the day of the test. Re-taking would give you another opportunity to show your full potential!