You finally took the GMAT, and though your score was not bad, it was not what you had expected or hoped-so, not your best score, but certainly not so low that you need to take the test again. With a score just below where you think you should be, should you risk it all and take the test again? Well, the truth is that there is actually no risk in taking the GMAT a second (or even a third) time in pursuit of a better outcome.
If you do your best on the GMAT on your first try, you can rest easy and move on. However, if you do poorly or simply don't live up to your potential, go ahead and take the test again. Simply put, you don't need to worry that if you do worse on your second try, your target school will average your score down or worse, consider only your later, lower score. In fact, whether your score improves or gets worse, your target school will consider only your highest score, thereby eliminating any risk to you or your candidacy. So, if you score a 700 on your first test and a 670 on your second, you are better off than if you had scored a 690 on both.
It is worth noting that Dartmouth-Tuck tacitly encourages multiple attempts at the GMAT by allowing applicants to create a synthetic score on the GMAT. Tuck will take an applicant's best performance on each section of the GMAT (verbal or quantitative), even if the individual scores are from different tests, and will count them toward a single score that the school will calculate on its own.
So, relax and take the test again if you have time and, more importantly, can do better. However, unless you feel that you can improve, taking the test over and over again is pointless. You would be surprised how many people take the GMAT repeatedly without considering improvement at all.