Two major reasons behind it are you have applied to colleges of very high cuttoff and second you have applied to limited colleges only. So, apply to at least 15 colleges in serial order priority wise according to branches. Add branches other than cs, else some seats will be left and you won't get admission in your favorite college. There's an option of changing branch in 2nd year by securing good score in 1st year. And apply to some private colleges also after completely filling government colleges.