Deciding Food Amount Ahead of Time

I am working my way through the Stop Overeating videos and have become very hung up on the idea that I need to plan out how much to eat ahead of time. How do you do this when you don’t know how hungry you will be? What if you finish that set amount of food and are still hungry?

I think it already seems like a lot to be avoiding all snacks and only eating twice a day. I think I am worried that if I don’t eat enough at the meals I will either be hungry until my next meal (which may be a long time away) or will end up snacking and not following through on that piece of it.

Thanks in advance for your help!