Ummm...help?

Ok...So, I'm in my brothers wedding next October.  It's a huge honor, and I'm excited, but I found out the what bridesmaid dress looks like:

Ok...I'm not a size 2...I'm overweight and well-endowed.  I'm really nervous about this dress.  I have no idea how I'm going to wear a bra...and I NEED to lose a considerable amount of weight so that I don't feel like a cow in the dress.  HELP ME!!!!!  Please...tips, advice...Anything. 

Thank you.  :)