It is difficult to say any comment about it ,because it totally depends on the difficulty level of exam of that day .

But on my past opinion if you deserve 81 percentile in jee 2021 than Yor marks varies  around 50 to 60

Hello dear, 

According to given percentile in jee mains the general rank will be approximately close to 1.7lakh ,it is hard to predict the marks with percentile  but your marks will be less than 90 as predicted from previous year trend rank is marks.