If you are already scoring 150 in mock tests of BITSAT, then reaching to a score of more than 200 is not a big task as you can easily reach it by following a few practices:

1. Always check your calculation and perform them slowly
2. Have confidence and do not spend time on question unnecessarily.
3. Know which questions to leave as some questions are designed to eat up your time.
4. Always practice with a clock and identify areas where you are spending disproportionate time
5. Maintain your sleep schedule as it affects you a lot!

Hope I have answered your question. All the best!