Hey there,

I understood the confusion you are facing. The basic idea of percentile is to compile the NTA scores of multiple session papers. Some students may feel like they have faced a difficult question paper for their session and the other session paper was easy. So to make sure that all students are given equal priority (in terms of difficulty ). If the paper stands out to be easy then the percentile needed to qualify is increased and if difficulty level increases then changes are made accordingly.

In your case, the marks you obtained are good. May be the paper you faced was easy and many students were able to score well ,so your percentile is low.

If you are curious to know more :

https://engineering.careers360.com/articles/jee-main-marks-vs-percentile

Hope this clears your doubt..

This can happen if the more number of students have scored good high marks. Also you must see the previous year marks vs percentile analysis to expect what your marks could come.Even you could also see the youtube videos on marks vs percentile so that you could predict your percentile.