For improvement exams, the marks are only added to the results else no changes are made. SO if you don't go for the exam then you will get the same result as you have before.

See if you think you need some improvement in your result then I would recommend you to go for it undoubtedly. If you score less than your marks obtained before then also your new result will have the previous year marks. So you have nothing to loose. So if you can go for the exam.

To know more about Improvement exam visit the link below:

CLASS XI: https://school.careers360.com/news/cbse-10th-improvement-exams-2021

CLASS XII:

https://news.careers360.com/cbse-hold-class-12-compartment-and-improvement-exam-2021-from-august-16

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