Hello, 420 score in NEET is not sufficient enough for you to get an admission into a medical college. Looking at the last year's cut off marks in the medical colleges of Tamil Nadu, it is very difficult for you to get an admission. The minimum requirement of marks for medical admission is at least 500. 

I suggest you prepare for the NEET 2020 from now onwards with equal deidication and hardwork. 

All the best.