Rachel London

I need to pay back some of my child benefit payments from tax year 21-22. I received all payments for one child which the form calculates as £1099.00 However I actually received £1099.60. I followed the steps to add in a differing amount, but it won't accept this. Whenever I go back to review, it's changed the amount to £1099.00 again. I really just want to submit my form and pay. Can I just add a note in the box provided? Thanks for your help!