I prepaid my filing fees but am still being asked to pay the full amount to file.

Are you using the exact same User ID that was used to pay for the online edition?

See this TurboTax support FAQ for checking your fees - https://ttlc.intuit.com/community/charges-and-fees/help/how-do-i-review-my-fees-in-turbotax-online/0...

Close all TurboTax windows on your web browser (including this one).  Copy and paste the account recovery website link onto a new web browser window and run the tool.

Use this TurboTax account recovery website to get a list of all the User ID's for an email address.  Run the tool against any email addresses you may have used - https://myturbotax.intuit.com/account-recovery

If none of the user ID's received will access your 2020 account, then use the option shown in blue on the account recovery website, "Try something else"