hi,

see you are eligible to give jee main exam for three time, that is 2020,2021,2022, now coming to your 12th score percentage, you are not eligible to apply for nits, iits or cftis, since the qualifying marks recruitment is 75% aggregate in 12th score for general candidates. however there is many more colleges available which offer admission in btech courses though jee main score. you need to study the full syllabus of physics chemistry and mathematics , I suggest you once revise the topics from text books , then solve mcq questions from arihant experts mcq books, also you may join careers360 knockout program to know about important  topics lectures and model questions.

https://learn.careers360.com/knockout-jee-main-april/