I'm very happy that you are getting ready for your surgery and getting the help that we ALL need at some point, I struggle a lot the first month after surgery about how I ate, if it was enough for me, for my body, etc. all crazy ideas, in some point I learned that after surgery I START eating better even in portion, I'm more selective of what I eat, and eat a lot haha, your just afraid about the change! and that's normal as a human we are afraid of what we don't know, but believe me that emotion its going to come off ass soon as you lost the first pound!
Xoxo - best of luck