A MCAT of 510 is a good MCAT and you have an excellent GPA. If you could add to your clinical volunteering hours and start shadowing then your application would be stronger. It would help to apply more broadly and I suggest schools such as:
Quinnipiac
Vermont
Albany
NYMC
Hofstra
Drexel
Temple
Jefferson
Penn State
GW
Georgetown
Oakland Beaumont
Western Michigan
Rosalind Franklin
Loyola
Creighton
Tulane
UA (Phoenix and Tuscon)
Roseman (new schools accepting applications sometime this year).
Of course reapply to SLU and SUNY Downstate.
The GPA-MCAT grid shows you have a 80% chance of a MD acceptance. The 20% who are not accepted are usually those with red flags, late applicants, applicants who apply to too few schools or too many reach schools, or have weak clinical volunteering or shadowing.