Inglorious bassterds-spoiler

When I watched 5x17 inglorious bassterds,, I couldn't believe it, this episode got me. I couldn't believe what these characters were doing, and the lengths they would go to,and the depths they would sink. My heart broke for blair and at the point I couldn't look at chuck. It served as a great catalyst(or part of one anywa)for the transformation in season 4 and 5. The emotions were tense in this one, but there's one thing dont understand. If chuck set it up with Jack ti seduce blair and get to keep his hotel, then why does he have a look of surprise at nates party when serena isn't with blair? He manipulated her ans told hack how to get to her during the whole thing, so if thst was his goal and what he wanted, why is the look on his face when he talks to serena and runs upstairs and find the dress box one of astonishment abd disbelief, like he didnt know? Was he truly hoping she wouldn't go through with it?