Hi

Appearing for JEE advanced examination doesn't mean that you becomes ineligible for taking admission in college based upon percentile or rank obtained by you in JEE Mains examination so you don't need to worry at all.

You will be able to take admission in NITs and other colleges based on your performance in JEE Mains examination even if you don't perform well or fail to qualify JEE advanced examination.

Now , that you still have time left for your jee examination I'll suggest you to focus on your preparation and revision,  go through mock test paper sample papers and previous year question papers of jee as it will let you know your preparation level and and weak areas so that you can work on them and perform well in your examination.

THANK YOU