For admission into the government college you should score above 500+. The admission also depends upon15% all india quota nad 85% state quota seats.

As you said you expected to get 420 there are low chances of getting the colleges through AIQ.

As the admissions procedure changes every year depending on seats available you may get the seats in state quota level.

For better prediction check into the link given below

https://medicine.careers360.com/neet-college-predictor?icn=QnA&ici=qna_answer