Yes it is easy to qualify BITSAT as it is easier than Jee mains and advance. Well if you are planning to opt for CS than you should also study hard enough to get that. Try practicing sums from books like HC Sharma and remember the concepts that you learn. If you are not confident in physics make sure you are hoigat chem andChen and maths because that is where you can score for marks in physics. As this exam also checks your speed and accuracy be quick in solving the sums. You get 180 min to solve 150 questions but the difficulty of all the questions are easy. 

All the best!