Hello Aspirant

According to the rule,you are eligible for JEE exam in either of the two ways possible

1.Score minimum of 75% in your boards

2.Be in the top 20% of your board even if you have not got 75% marks,The 20 percentile cut off varies from state to state

So getting 75% is not always the barrier even if you are in top 20 percentile,you can get through JEE counselling

But if you don't satisfy above criteria you are not eligible no matter how much you score in JEE

for more info:

https://engineering.careers360.com/articles/top-20-percentile-of-class-12-boards-for-nits-iiits-and-cftis

REGARDS!