Hello aspirant!
Hope you are doing well!

There is no need to be demoralised based on your 12yh board marks. They have absolutely no effect on your NEET score. You have to have good fundamentals of class11 and 12th. Mostly students take coaching of 1year or 2 from coaching institutions and qualify for top level government college.
Refer to following article
https://medicine.careers360.com/articles/how-score-good-marks-in-neet