I cannot answer whether your 680 will earn you admittance into your desired school - - there are highly qualified admissions consultants here and elsewhere ...but I can assure you that eliminating anxiety is the quickest and easiest thing to do in preparing for the GRE, GMAT or any high stakes test.

Happy to share more if you go that route.

I'm also teaching a free 1-hour anxiety relief session, the information is here: https://www.facebook.com/events/236804927372602/

and registration here:

https://tinyurl.com/SelfCareinCOVID19

Well, there's 680 and there's 680. Granted your Q is a bit low for your demographic, but GMAT alone is not the sole criterion for admission to top business schools; on the contrary, admissions is a holistic process. What do you bring overall? And where are you headed, and why is this school the right school for you? Specificity and research, that's the name of the game.
Now, how do you build that out? Certainly working with a professional admissions consultant can be helpful. These Covid-19 times bring opportunities as well as impediments; you won't be able to travel to the US to visit your top-choice schools, but there are a lot of on-line options. Most schools are hosting more and more effective 'virtual' class visits and info sessions.
Reviewing the schools you got dinged from last time, I'm guessing that some of the legwork was missing in your applications. You should be able to be a strong candidate, with some well-targeted research. if you target your applications well and make the most of your leadership and professional assets, alongside goals and school research, you should be able to produce a highly competitive reapplication.

Good luck!