I think everyone goes through the fears you are experiencing now, I certainly did.
A couple of things my surgeon said, things I've read, etc... The latest thinking is that people's brains tell the body to process food in different ways. For example studies of Prisoners of War should that they were all given the same meagre amount of food and took that same amount of exercise and yet, after years of being imprisoned, on release, some were emaciated and yet some were not. It is thought that in some people the brain tells the body to process food differently, to store more fat than in others. A stressful episode in someone's life seems to cause some people's brains to panic as it thinks the sudden shift might be the body going into starvation mode so again it stores more fat.
Then there is the issue of the hormone ghrelin that sits in your stomach ( the part that gets removed during surgery). In some people maybe because of constant on and off dieting this hormone, which sends a signal to the brain that you are hungry and must eat, goes into overdrive. I know that in my case most of my weight issues started around 5/6 years ago when things were a bit stressful. Since then, doing the same things I did before to lose weight, just didn't work. As soon as I started eating during the day, whether at Breakfast time or waiting until lunchtime, once I started I never felt full so kept eating.
So to my point (sorry a bit long-winded but I'm getting there..). I had all your fears. I was sleeved on 26 April so I am 2 weeks 3 days post-op and the part of my stomach containing Ghrelin has gone. I can honestly say that have an amazing calmness around food. As an obsessive daily weigher, I don't seem to have the same panic about the numbers going down, I just know they will. I have remained the same weight for 3 days now despite eating very little and miraculously it doesn't faze me at all. I feel back in control for the first time in a long time as I know I will lose weight. During this 3 day stall I am changing shape as my body adjusts and recovers from surgery. It's like my brain has been rebooted and the cravings, lack of weight loss panic, mild blues associated with being overweight have just disappeared... I have a friend who was sleeved in September last year who also described all of the above post-op.
So please don't worry. Unless you intend to consume a vat of ice cream at a gazillion calories, you will lose weight. Make healthy choices, walk more and above all enjoy getting this fresh start....