No, taking it a second time definitely won't be a knock against you. I don't know the exact number, but a lot of applicants take the GMAT more than once. In general, schools are willing to give you the benefit of the doubt, and they will take your highest score.
Just be sure that you're really ready the next time you take it. If you end up having to take it a third time, that could cause some concern among adcomms.
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