Did you at least select a non E+ seat? IMHO, it is best to select a seat and then try to change when things open up, then to be left with no pre-assigned seat. In the event of an oversale, and without sufficient volunteers, it's like musical chairs. The one without the seat when the music stops is out. PLaying roulette in hopes that one gets a seat upgrade is a risky proposition. While you win far more often than you lose, when you lose, it hurts far more than when you win. I know the agents said they were not oversold, but that can change rather quickly if other flights cncl or there are misconnects on earlier flights from UA or other airlines.