Without a score breakdown, and assuming your scores are evenly split, I don’t think I would recommend a third MCAT attempt. You already significantly improved over your first score. For an additional retake to make a difference, you’d likely need to 5 or 6 points higher. At 509, youre a couple points below the median for matriculated applicants. Luckily your GPA is good. I think you would have more success if you applied to more than 15 programs and had your applications in before September. You may still have success with DO programs this cycle.