Hello Madhumita,
Hope you are doing well.
The CAT cutoff of Department of Management Studies, IIT Madras for open category remains above 96 percentile. It was 98.2 percentile for open category as reported in year 2018 and 2019 which is very close to the cutoff of DOMS IIT Delhi though.
Yes, There is a exemption for those scoring above 90 percent in Graduation, but even to avail that you need to score above 90 percentile. Please, try little hard next year and nail it.
All the best.
Hope it helps you !
Thankyou !