Welcome, Gigi. We all felt fears like you're having now. You won't fail.
But surgery's not a cure.
The process of surgery and recovery will have major physical effects, for sure. The biggest part of your weight loss will happen right after. You'll be making adjustments to your lifestyle and eating habits immediately.
But you'll still have the eating disorders that led you to eat out of control so much that you've arrived at this point.
It's a good idea to read about nutrition and figure out how you're going to design meals post-op. That's how you'll succeed.
It's not a magic bullet. WLS is a leg-up that allows you to win more and suffer less. But you can defeat it, and some do, unless you commit to the new way of eating.
I lost so much weight so easily that I was motivated to change a lot of habits. Most notably, I became interested in hiking the wilderness, and I trained for big hikes 5 or 6 days a week at the YMCA. Having a reason to spend two hours on a treadmill accellerated my weight loss and toned my body.
Don't think of surgery as THE thing. It's only a tool. The THING is your mindset. Being fat actually makes people stand out in crowds. Sometimes it's hard to give up attention, even when its negative. The trick for me was my desire to become ordinary.
Affirmations work. Try repeating your deepest wishes in the form of affirmations all day long. See the powerful difference between "I want to be beautiful" and "I am beautiful." Keep repeating an affirmation until your inner gremlin stops arguing with it. You may think you can't believe it, but an unconscious part of your mind is starving for it, and hears every word.
Stop worrying. Have the surgery. Consult with your dietician and relevant medical and psychological professionals with an open mind. Allow yourself to believe, no matter how little you do. Follow the post-op plans. Accept what happens after, even the occasional little gains and slips.
We may understand your fears, but your unique set of compulsions and criticisms are yours alone. It's your journey. Create your own map and follow it.
You will not fail. You've already succeeded.