Most of the time its kind of hard to get through all the content in one session. Players dabble, and I often underestimate the amount of time everyone spends socializing, bonding, or even just exploring -- before progressing to the next plot point.

I need to get better at this too.

I've run two successful one shots with different degrees of success. The first I completely improvised, no notes or anything, and the ending did feel a bit rushed but we wrapped it up in one session. The second I ran with just one major theme in mind and the rest was improvisation. It helped that I set them up in-universe with the main campaign so the end goal was just to create consequences for the main party, good or bad.

I've always considered "one shot" to be "one story arc" like a dungeon or something rather than strictly one session, so I thought it was normal for them to take a few sessions, especially if you don't have time to play for 6+ hours straight.