Are you aiming to apply this cycle? If waiting until next cycle, I would strongly consider taking the MCAT in Jan or Feb 2018 (or any time prior to June 2018 when the cycle gets going). You just scored at the 61st percentile on the MCAT, and can expect ballpark similar on the real deal. It is unrealistic to expect much more than a 3 point change in that 17 days, though it is possible. Of course it comes down to "are you happy with this?"
With your sGPA, you probably have a shot at a wide range of DO schools. I am not at all sure about MD schools, given the cGPA. If you score ~503, I don't think you can expect much from MD schools.
If you delay your exam, study very hard and improve your practice tests scores, you could probably score much better. I would not be satisfied with a 503 if I were you, and would postpone test. But given your other stats, scoring around 503 would probably not be lethal.
