For what you're planning on going into (social responsibility/public sector) it's probably not going to make a huge difference -- Georgetown is known for it, it's in the ideal location (DC), and so you likely won't have a harder or easier time finding a job in that area compared to someone who went to a higher ranked school.
From your profile, you do have a shot at schools like Columbia and NYU, even with the profile you have as it is (although sure a higher GMAT would help and a course or two in college-level calculus that you can take through some extension program/night class) -- however, the fact that you got interviewed and waitlisted at one of them suggests that you were certainly in the mix -- you were close. So I wouldn't say it's just the numbers alone - but that your application could've been even stronger.
It's really a personal decision whether you want to wait another year. If your GMAT is 700+ and you take 1-2 courses in calculus/stats/econ/whatever math/ *and* you do an even better job on your application (including interviews), then you probably should be competitive for schools like Columbia, NYU, etc. and schools like HBS are a stretch (but still within reach). But there's still a risk that you won't get in - it can be a very subjective process, and for someone like yourself where it seems like the decision (admit/ding) could really go either way.
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