Crap, the bridesmaid dress doesn't fit!

I've shopped at at least a dozen stores in the Valley to no avail. I'm to be a bridesmaid in Haiying (one of my college suitemate)'s wedding Labor Day weekend. I saw this dress on sale, better yet, on clearance, at Jcrew.com. It fit the description - color, style, and fabric material - that she wanted. So, I took a gamble. I checked their size chart carefully before making a decision. A Petite 6 should fit.

It came via UPS this afternoon. I tried it on less than an hour ago.

My concern was that it wouldn't fit in the waist. After all, I had a baby ten months ago. It fit there just fine. Where it didn't fit was in the bust. My chest is WAY TOO BIG! Perhaps this is due to the fact that I'm still nursing five times a day. Maybe the dress is also cut a bit small in the chest. CRAP! Don't know what to do. Labor Day weekend is just a month and a half away. As she drinks less milk, my breasts should shrink, but by how much?!