Academically, your profile is average - a 680 GMAT and a 3.2 GPA. I like your story very much though, and think it makes a lot of sense based on your experience and background. In terms of professional experience, you're definitely a non-traditional candidate - but this can be overcome. I think you just really want to showcase your leadership and team capability (seeing as how you haven't worked in professional business/corporate environment, you need to show that you have the skills to lead within than type of structure/organization.). The other thing you should really be aware of is that right now, your profile is somewhat one dimensional (all your extracurriculars/community work are very much the same as your professional track/goals. This is what makes your story strong and believable, but at the same time, you need to show what else you are besides a social impact/healthcare person.) You need to show your personal interests/passions and multi-dimensionality-- are you also a marathon runner? Lead singer of a band? Soccer coach?
Duke is a great program and I think it's a smart choice, but I don't think you're a shoe-in there given your academic profile, lack of business experience, and lack of balance. It's definitely possible though, and should stay on your list. I'd also target some safer programs like UNC, UCLA, University of Washington. Kellogg, Haas and Wharton have great programs, but may be reaches... could keep Haas on the list as your reach school, but depends on how you want to hedge your risk.
Hope this helps,
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