Hi there,
Sorry to hear that GMAT didn't pan out the way you wanted. Given that you're looking to apply to schools in Germany, your score is actually within average score for most of the schools in Germany except for the top MBA program, Mannheim, where the average GMAT is around 680. The average score for the #2 school in Germany, ESMT Berlin, is 640.
That said, there are other factors that come into play which could make your overall application stronger, most importantly the depth of your work experience, quality of your recommendation letters, and strength of your essays. However, if you want to aim for Mannheim or be in the "safe zone" for ESMT Berlin or HHL, retaking the GMAT to aim for a 680 is not a bad idea. Also, if it was your first time taking the GMAT, chances are you might have had an "off-day" and there's still potential for improvement. However, if it was your third time taking it then you might have reached your max score. Taking it the fourth time is a big maybe, but not worth the time and effort for fifth time. Hope this helps!