Hello Buddy! Hope you are doing good.

As you are enrolled in an institute and simultaneously doing your JEE preparation for appearing in JEE 2021, when you take part your admission through JEE 2021 counselling then after allotment of seat when you take admission then you have to again study 1st year in the alloted institute through JEE and also have to withdraw your admission from the institute you are not studying in. For knowing your possibilities of getting a seat you can use the college predictor tool given below :-

https://engineering.careers360.com/jee-main-college-predictor?utm_source=qna&utm_medium=jee_cp

Hope this will help you.

ALL THE BEST! WORK HARD !!