How do I know if my Costco purchased software was used for my filing? I did include the code, but still ended up paying $110 for both federal and state filings.

Then it wasn't.  And there is nowhere to enter the 14 digit License Code.    You did not use the CD/Download program you bought.  Did you install it?  Sorry you can't apply the Desktop purchase to the online version. They are separate things and don't talk or sync to each other and are priced differently. You would need to get a refund for the CD and pay for online separately. And state is a separate additional charge in online.

The software you purchased from Costco was supposed to be installed on your personal computer so that you could complete and file your tax returns using the installed software.  The License code could only be used with the installed software, not using the TurboTax online web-based editons.

Since you completed and filed your 2019 tax returns using the TurboTax online web-based editions and not the software you purchased from Costco, you should return the software to Costco for a refund.

What can I do if Costco won't accept my return?  I read there was a 60 day satisfaction guarantee?  Would Turbotax be able to reimburse me?

Thank you