Man, I can be so stupid. I planned out my whole bus trip to the airport last night, ahead of time. Was very proud of myself. In doing so, though, I forgot that buses here have different schedules on weekends than they do on weekdays, and didn't notice that I was looking at a weekday schedule. Turns out that the route I need doesn't run early enough on Saturdays to get me there on time.
Hooray for Alex, who is rescuing me and giving me a last minute ride.