No, you can appear for JEE Main exam in your 12th class or after completing your 12th class.

Below is the eligibility criteria of JEE Main exam you can check

- Students who are born on or after October 1, 1993 are eligible to apply.
-Candidates belonging to Scheduled Caste (SC), Scheduled Tribe (ST) and Persons with Disabilities (PwD), should have been born on or after October 1, 1988. Candidates of these categories have been given a relaxation of 5 years.

- Aspirants should have passed 12th class

-Students, who are appearing in class 12th

-It is mandatory for aspiring candidates to have taken 5 subjects in 12thor qualifying exam-The 5 subjects for B.Tech/B.E. are: 1-Language, 2-Physics, 3-Mathematics, 4-Any one of (Chemistry, Biology, Biotechnology, Technical Vocational Subject), 5-Any other subject.

-For admissions to NITs/IIITs/GFTIs, candidates should have secured at least 75% marks in class 12th exam or be in the top 20 percentile in the class 12th exam conducted by the respective boards. For SC/ST candidates, the eligibility criteria is 65% marks in class 12th.   

-A JEE Main aspirant can avail 3 attempts for the national level undergraduate engineering entrance exam.

Good Luck!!