Sir I'm  a district topper

See this is dicey to answer as it generally changes from year to year. I can just maybe give you an approximate idea. If you wish to get into the top colleges anything less than 500 marks will be tough. CS is pretty popular and chosen by many so ideally anything above 450 will surely fetch a good college.  You could check the cutoff of the previous years to get an idea of the ranks that got CS allotment and figure it out. https://engineering.careers360.com/articles/upsee-cutoff