A few thoughts:
1) with interviews at Harvard, Einstein, and Miami, it is highly unlikely the OP has any major deficits in application, including ECs overall, writing of either primary or secondaries, or LOR.
2) having 3 interviews is average for accepted applicants.
3) talk of post bacc or masters borders on wastefully foolish
4) talk of being a reapplicant is quite premature in this case.
5) we have no idea what your school target list or indeed how many schools you applied to
6) nor do we have any idea what your EC array is
So before you panic and before you look for suggestions, tell us the rest of your application
My school list is the typical list advised here on SDN with some reaches:
Tufts School of Medicine
Boston University School of Medicine
Albany Medical College
Albert Einstein
Brown University
Harvard
Hofstra University
Icahn School of Medicine at Mount Sinai
Thomas Jefferson University
New York Medical College
Pennsylvania State University
Quinnipiac University (Netter)
University of Connecticut
University of Pittsburgh
University of Vermont
Yale University
University of Rochester
Drexel University
Temple University
University of Buffalo
My EC array includes:
285 hours paid non-medical experience
1000+ research hours (3 posters, no pubs)
93 shadowing hours (internist, anesthesiologist, radiologist)
170 hours working with underserved (elderly, migrant farm workers, building homes for low-income residents)
176 hours volunteering at a hospital, 40 hours working as a medical assistant (216 clinical hours)
150 hours tutoring/mentoring
All activity durations are at least 3 semesters long