A student can Appear for UCEED for 2 consecutive years that is a standard 12th student and a 1st year or a pass out a year ago 

Hello aspirant.

For applying any entrance exam u must be studying in 12th or have completed that. Since u are in class 11th now so u would be appearing in that exam in 2020. 

If u failed to succeed in that year then u can apply for another chance but u should be taking a drop or studying in 1st year of the college. But when u get admissioned in the college under UCEED u would be joining in 1st year itself whether u have completed that one in previous college no matters.

Hope u got ur point. Ask if u are having any doubt regarding this.

Good luck