Hii Archita, though your qualifying percentile will vary according to the number of obc students appearing for the April session of JEE mains. But the predicted average cutoff range for general category on the basis of various analysis by different coaching institutes is 75-78 percentile and the cutoff for obc category is always less than the cutoff for general category so you can expect your cutoff to either be less than this or betwwen this range. If you want to calculate the rank you can use the normalisation formula = (100-your percentile)*total no. of students who appeared for the paper/100.

If you want any other information about the normalisation formula, you can check out the following link-

https://engineering.careers360.com/articles/jee-main-normalisation-process-how-scores-are-calculated

I hope this would have helped you. All the best!