I know it's not quite what you wanted, but 660 is within one standard deviation of 680 - technically, there's no statistically significant difference in those two scores. And 660 is still a very good score, so don't be so discouraged! Give yourself some credit for doing that well - that's better than 85% of the population. That doesn't mean you won't set your sights higher and try to do better next time, if you want to take it again - but do give yourself some credit!