There is a chance that filling the wrong roll number on the CUET OMR sheet and writing the correct one in the blocks might affect your result, but it shouldn't necessarily lead to disqualification.

The OMR sheets for CUET are scanned electronically to capture the marked roll numbers. If the electronically scanned number doesn't match your actual roll number, it could create a mismatch during result processing. While writing the correct roll number in the blocks is a good step, it might not be directly captured during the electronic scanning process

https://university.careers360.com/download/ebooks/all-about-cuet

I hope it helps!