Hi

It doesn't matter even if you have failed in your 6th subject, provided you should have passed in overall with 5 subject and your result status should be 'PASS' in your result/marksheet. and don't worry you will be able to take admission in NIT provided you should have passed 12th in overall in 5 subjects including Physics,  mathematics as compulsory subject along with anyone of Chemistry or Biology or Biotechnology or Technical Vocational Subject.

Also,

To be eligible for NITs one needs at least 75% marks in class 12th if belongs to General or OBC category  or at least 65% marks in class 12th if belongs to Sc or St category. For this year i. e 2021 this minimum percentage requirement of 75% - 65 % has been lifted off.

So, even though you have just got 57 percent in your class 12th board exam , you are still eligible for admission in NIT after qualifying JEE main this year in 2021 .  But, do not that percentage barrier of 75 - 65% will be there in 2022 and then you won't be eligible with your percentage

For detailed information about jee main eligibility criteria  go through our page, the link for which is provided below

https://engineering.careers360.com/articles/jee-main-eligibility-criteria

Thankyou