Comp Science is the most preferred branch and with IITBombay the rank closes well belpow top 100 which correlates to score of 305+.

This calls for great preparation strategy and absolute deication plus smart planning.At least try to solve 60 problems from day 1 including PCM.As and when you go ahead, make sure you give alot of mock exams and analyse them reguklarly to avoid repetitive mistakes and keep revising such problems where you find yourslef weak.

some top books recommended by toppers are:-

Physics:- 

Concepts of Physics Vol I and II by H.C. Verma

.New Pattern JEE Problems: Physics by DC Pandey.

Chmeistry:-

Organic Chemistry by O.P. Tandon

Numerical Chemistry by P.Bahadur

Mathematics:-

Maths by NCERTBOOKS.

Solvibg atleast 200 questions from each important chapter will eliminate your doubts.

the folowing tips shall help you out in achieving your goals.

https://engineering.careers360.com/articles/jee-advanced-preparation-tips-physics-chemistry-and-mathematics