Yes definitely you are eligible for JEE Mains 2020 if you have not appeared for it thrice. As National Testing Agency (NTA) has declared that a candidate can only appear 3 consecutive times in JEE Main and twice in JEE advance. Don't lose hope prepare well this time. Best of luck. 

Hi!

Dear aspirant, it all depends on how much time have you give JEE-MAINS paper, if you already give JEE-MAINS paper three times then it's not possible for you to give JEE-MAINS paper again, otherwise you will give your JEE paper again. It's simple.

Thanks!