You have nothing to worry about the marksheet even if you failed in it. See Improvement examination is only for the improvement of marks and as a result, if you fail then also there will be no impact on your marksheet. You can use your previous marksheet as the final one.

To know more about CBSE Improvement examination visit the link below:

https://news.careers360.com/cbse-improvement-exams-2021-check-class-10-12-date-sheet-eligibility-criteria-here

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