See BITSAT is an entrance exam that leads to the admission to the best private engineering college of our country. So you can well imagine, the level of toughness or level of question it gives to students. I am not trying to demoralise or frighten you, but this is the truth. during our time(2015) the cutoff to get  CSE branch of engineering was 369 for Pilani campus. And surprisingly many students meet the criteria. So you can well imagine the competition out there. Just completely solving the Arihant books or just sticking to solving previous years papers will not sufice if you want to crack the exam. You have to be thorough with the PCM subjects. Do the completion of books(more than one books), solve papers, give mock tests, learn time management because the number of questions is huge, and practice high level questions like JEE mains. I am sure if you follow these guidelines you can surely touch the cutoff criteria of some or any branch.

Best wishes for your exams!!!