8/21 is the date and it does look like the flight I want may be completely sold out (and the flight they put me on-I swear I saw these earlier)? I still can't get it to give me any afternoon flight that day without an overnight connection even on Google flights, or even show up on United.com even though the flights from DEN look wide open and the 130pm flight JAC-DEN seems to have seats. It does show up on the mileage options though, so I guess there's that.

Looks like my best bet is to cancel and re-book on AA.