The best advice that I can offer is to breathe and remember why you are having the procedure.
I, too, freaked out a couple days before surgery. I thought to myself that if I am losing weight without having my anatomy altered, then why do it. Then I remembered that I also struggled for so long and give up when it seems as if the weight wasn’t dropping fast enough. I also remembered that I don’t want the diseases associated with obesity. Just remember your “Why”.