I misspoke in my previous reply. Entering the contributions made through payroll also as personal contributions produced a deduction on your 2020 tax return to which you were not entitled. Assuming that this deduction affected your tax liability, you'll need to amend your 2020 tax return to correct that. If you don't amend your 2020 tax return, there's a good chance that the IRS will detect the error and bill you for the balance due for 2020.
Since there wasn't any Form 5329 included in your 2020 tax return, none of this affects your 2021 tax return.
