The expected cutoff for Gen EWS category in Jee mains this year is around 70-75 percentile. This is just the estimate according to various factors like paper difficulty level, no. Of students appeared,etc. While scoring around the cutoff will not assure you a good nit/iiit, your ews rank should be above 2000 or 97 percentile + to get a good branch in a top college.

Good Luck !