The Application Process

Obviously, it is known that the GMAT is very important to the application process (I am on this website, after all), but how important?

I have a semi-unique situation. I have not graduated Undergrad yet; I am applying for my Masters of Accounting (MAcc), not my MBA. I realize both programs have a relatively different set of "requirements" for applicants. I know the GMAT and work experience are the 2 most important things for an MBA application; does anyone on this forum have knowledge of what is most highly regarded for MAcc applicants?

Here is my profile:
GPA-3.68
Accounting GPA-3.74 (4.0 in Intermediate Accounting - highest class taken thus far)
Letters of Rec from Intermediate Acct. Professor and Partner at regional Accounting firm where I interned last winter.
Projected GMAT score (taking in 2 weeks): 650-670

I want to apply to the University of Michigan MAcc program, and if I achieve a 680 on the GMAT I don't think I will have a problem (school site says 670-680 is average GMAT score for MAcc applicants), as my GPA is strong. However, I have scored <650 on a couple practice tests, and if I have a bad day on test day, I'm not sure what I should do after that. If I score a 640, am I basically forced to re-take the exam?

This is the reason I am asking about the weight of each part of the application. If anyone has any knowledge regarding this topic, preferably for MAcc applications, please share! Thank you!