An admissions team will not frown upon you not taking the GMAT test again, but your GMAT score is significantly below the averages of the schools you are applying to.
As an example, for Chicago Booth, 80% of accepted applicant's GMAT scores fell in the 660-760 range. This would mean that your GMAT score would be in the bottom 10% of applicants.
Your GMAT score is self-reported, so an admissions team will focus on your highest score. I know you may have had difficulties with standardized tests in the past, but remember that the test is beatable.
If you are set on applying to the schools you are considering, I would recommend that you take the test again. This is not to say it is impossible to be accepted with a 640 test score, but it will be much more difficult.
Hope this was of help.
Conrad and the Stacy Blackman
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