If you are thorough in NCERT Biology and assuming you have completed all questions of NCERT Exemplar and you do not do silly errors, you can easily get 320+. 

Solve previous year (past 10 years) medical entrance question papers (NEET and AIPMT).

Solve NCERT Exemplar Questions if you haven't solved it.

Do questions from MTG Fingertips Biology.

Previous year in 2018, 82 questions had come from NCERT and out of remaining questions, 3-4 questions can be solved if you have understood each and every line of NCERT Biology.

Thank You

Best Of Luck