Feel extremely bad!!

I just turned down one of the best opportunities in my career!! 4 weeks ago, I got a message from my supervisor asking me if I am interested going to Salt Lake city to work on a project for 3 months. I will work 10 days and 4 days home (or fly me to the other city). Then I was so excited and told him yes. However, we haven’t heard anything from the other office since we sent them e-mail 4 weeks ago. Then I thought that it wouldn’t happen. So I got Acorn 1.5 weeks after that. This morning I was talking to my teammate about that project, he asked me if I heard anything about it. I told him that I didn’t hear anything and I think I will not going since I got a puppy. So I said that I would talk to my supervisor about the situation. After lunch, my supervisor came and told me that the other office called and wanted me to get there by the beginning of May!!! My supervisor told them that I should be able to do that (that is the bad part)!!! I was so embarrassed about that cause I should say something in advance. I feel so bad about that. I told him the situation and it is really hard for me to leave now since Acorn is just 2 months old. He suggested to bring the puppy with me but I think Acorn is still very young to travel with me 6 times in 3 months. I told my supervisor that I maybe able to work it out if I can start in June so Acorn is 3 months with all the shots. I can bring him there every other trip. I feel so bad about that (not because I turned it down, because I didn’t tell my supervisor in advance). It is really not my day today!!!