See if you are final year appearing student then only you can apply for CAT 2021 and for that you have to choose the option for Appearing candidate of graduation while filling up the application form. Now if you are in 5 th sem you aren't eligible. If you are only in 6th sem of  your 3 year course and you have given the exam or will be appearing in the final year examination then only you are eligible.

To know more about CAT2021 eligibility visit the link below:

https://bschool.careers360.com/articles/cat-eligibility-criteria

I hope this answer helps. All the very best for your future endeavors!