since your main focus is BITSAT you should focus on preparing :

1. be thorough with NCERT specifically for chemistry .

2. cover important question of mathematics from RD Sharma and clear you concepts from NCERT, it is must to be done.

3. for physics try to cover all topics from NCERT and try to solve questions from HC Verma.

4. most important part of preparation for BITSAT and JEE Mains is to practice previous year question papers , they are  a must to do, solve as many past year question paper as possible .

5. cover all the study material from your coaching institute, this will boost your performance not only in JEE Mains but also in BITSAT.

so, just keep on doing maximum revisions, do not forget to complete ncert and solve past year papers of both JEE Mains and BITSAT. Then also give mock test to check your current level of preparation.

hope this helps.