Hello

To get into a good Engineering college, you have to score well in JEE MAINS which is an exam for Engineering. Having 75% in your class 12th boards is the eligibility criteria for sitting in the exam. Your class 12th marks won't be calculated. The admission in an Engineering college is only through JEE MAINS and admissions only to IIT depends on the percentile you will secure in JEE ADVANCE exam.

For more details, kindly check the given link.

https://engineering.careers360.com/articles/jee-main-application-form

Good luck.