GMAT Strategy

Your range is within one standard deviation of 680 on the tests, so generally, yes. There is a little bit of luck involved on test day, both in terms of how "on" you are and in terms of the mix of questions you happen to get (how well those questions match your strengths and weaknesses).

You certainly seem within range!

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!