According to JEE Main eligibility criteria, the candidate should possess at least 75% in the Board exam for getting admission in IITs and NITs and other IIITs,
But you don’t have to get demotivated because there is a way through which you can sort this out.
You can give the NIOS exam which is conducted several times a year, so you can give the exam anytime you want. And the marks have the same authority as of CBSE or any other board. So cheer up and give the NIOS exam and get good marks.