Why does Auggie leave the school tour earlier than he planned?

Auggie is anxious to leave because of the way Julian treated him during the tour.

“Yeah, let’s just go,” agreed Charlotte, following Jack down the stairs to the next floor. I started to follow her, but Julian cut right in front of me, which actually made me stumble backward. “Oops, sorry about that!” said Julian. But I could tell from the way he looked at me that he wasn’t really sorry at all.

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We said goodbye kind of quickly after that. I think Mr. Tushman was a little surprised that we were leaving so suddenly, and then I wondered if he would blame Jack and Charlotte, even though it was really only Julian who made me feel kind of bad.