Hello aspirant,

The eligibility criteria for JEE Mains as set by the NTA is as follows:

1. There is no age limit.
2. You need to pass12th Board Examination or any equivalent qualifying examination with Physics, Mathematics as compulsory subjects along with Chemistry, Biotechnology, Biology and technical vocational as one of the subjects.
3. For applying in 2021, you should have passed your 10+2 exams in the year 2019 or 2020, not before.

Since you have completed your BSc for 3 years, that means you were a passout in the year of 2017 or 2018. In this regard, you are not eligible for JEE Mains.

Hope this helps you!