No, you don't have to report the 1099-Q if you used the entire distribution for eligible expenses and no, it is not too late to amend your 2020 tax return. If the distribution doesn’t exceed the amount of the student's qualifying expenses, then you don't have to report any of the distribution as income on your tax return. If the distribution exceeds these expenses, then you must report the earnings on the excess as "other income" on your tax return.
The Internal Revenue Service limits the amount of time you have to file a 1040-X to the later of three years from the date you file the original tax return, or two years from the time you pay the tax for that year.