Since you are preparing for BITSAT , you must be preparing for JEE also (most of the students do ) . Your JEE preparation must be thorough. For Physics , the series by DC Pandey is good. Chemistry - NCERT is the best . Search small hidden facts and make small questions from it. Maths - you may follow the book which you are following now , or can refer the set of Arihant books for JEE - they are sufficient . Once your concepts are clear , I think you’ll not need any extra book for BITSAT. I’m not saying don’t solve any other book , Arihant’s book for BITSAT is undoubtedly a good book but solve it after clarifying your concepts. Solve it as a practice book rather than a preparation book .

Focus on your concepts first , make them crystal clear . Solve a variety of problems , so that you become confident in your JEE Preparation.

Never ignore NCERT books . They are extremely important from the JEE and BITSAT preparation point of view . Many times they frame questions based directly based on the NCERT text.

You must also join an online test series . This is the most important part of BITSAT prepartion .

Thank you do well