The fact that the 529 plan shows the money dispersed in 2020 should be enough to satisfy the IRS (if ever needed), even though the school didn't credit the money until 2021.
In the 1098-T screen, click on the link "What if this is not what I paid the school" underneath box 1. You will then be able to enter the actual amounts paid.
As Irene2805 said, be sure to adjust next year's 1098-T, when you enter it on your 2021 return.
