Pre Op Visit Complete

I just completed my pre op visit. I am officially registered and ready to go for surgery August 31st. I have to admit that I am getting nervous and even find myself wondering if I am doing the right thing. I guess my biggest fear is that I am about to undergo major surgery and what if it doesn't work? What if I go through all this and I don't succeed? I know that I will lose the weight. I know that I am committed to succeeding but what if my body doesn't cooperate? I am terrified that because I have hypothyroidism, I won't be able to lose as much as I want. (I'm hoping to lose 100 pounds). I know it's probable pre surgery jitters talking but I can't help but worry.