You CAN do it. You looked into the surgery and you've done everything you've needed to get a surgery date, which means it was something you wanted.
I know the feeling though. I felt like I would somehow fail at this surgery (a surgery that is basically guaranteed to help you lose weight) as I have with other diets. Or, I believed I would somehow ruin my post-op diet.
After surgery you'll feel different. Obviously, you'll be the same weight, but those cravings will be gone. My doctor kept reassuring me of this, and I didn't truly believe him until after the surgery. You think you'll miss those trips to your favorite fast food restaurant, or midnight Snacks, but I promise you, you won't even think about them. Don't think of those "last meals" as "last meals." Granted the next couple months after eating will feel like a chore, you'll be able to eat them again some day, but a much smaller amount, and probably in a healthier version.
Don't be nervous! Your life is going to change, and for the better.