Was it "too tall" on one side, or just right on that side and too low on the other? That's the way it usually is for me. It's not that the tire bead is not properly in the rim on the "high" area, it's that it is too low in the rim in the "low" area. If that makes sense. I was told early in the game, and have always pumped it up to at least the maximum on the side wall, or a bit above that, to get those low areas to pop up in the rim. Just did it with some tires last night. I think if you search the web for how to deal with this, that is one of the typical suggestions, along with manipulating the bead as you go along.