I think you have a problem with the refinanced amount plus the highest outstanding balance in the last year being greater than $50,000. The highest outstanding balance in the last year was probably on the day before the first repayment was made in 2021, so take $50,000, subtract that amount, and the difference should be the maximum they can add by refinancing.
The loan payments do have to be level throughout the term of the loan, so for all remaining 69 months. If the new payment is at least equal to the amount that would be needed to amortize the additional loan amount over 60 months on its own, then you should be fine. For example, it would be a problem if the outstanding balance on the original loan was $1,000, and they wanted to add $40,000 by refinancing. The amount that would amortize $41,000 over 69 months would not be enough to amortize $40,000 over 60 months.