To remove the error I went into Forms mode and deleted the Charitable Organization Worksheet. Then on the Form 1040 Worksheet for Line 12b removed the $300 amount so Line 12b is now blank (empty).
Going back to Step-by-Step I completed the Deductions & Credits section without entering anything for a charitable donation and click on Done with Deductions. Continuing through the screens until landing on the screen labeled Charitable Cash Contributions under Cares Act, I entered $600. Continued through Final Review without error.