Hii,

JEE Mains is a National level Common Entrance test to get admission in NIT's and IIIT's. Yes, You can still write the JEE Mains 2020 exam. If you are qualified in the JEE exam and got a seat , you have to study from the first year. As you are in first year of Btech focus more on the JEE Preparation rather than your Academics. But make sure that you must pass the first year subjects.

See Abhay, whether you have to appear for jee mains in the next year completely depends on you, it's you who knows if you can prepare for it well . But in my opinion , i should say if you are in first year btech , you should not apply for mains the next year . You already have a good college and give your focus on you present btech , do well in it, score good cumulative percentage and complete your btech. Focus on what you have now. I hope you ll choose best for yourself!