My estimated score in WBJEE 2021 is 85.66. Would it be possible for me to pursue CSE in Heritage Institute of Technology?

You will almost certainly obtain it if your rank is within 3500. According to the marks you have, you have a good probability of succeeding. 

If you are unable to enter Heritage, do not hesitate to enter Techno India Saltlake. They have also delivered fantastic placements in both CSE and IT this year. I wouldn't recommend IEM Saltlake because it's more strict like a high school than a college.

If you score 85+ marks, I believe you will be eligible for Heritage.

So in the end, I would only suggest to you that it varies year by year that how many marks are required, and as competition is increasing with each day, only your hard work and dedication towards your dream can land you in a good institute.