It sounds like you dont just have anxiety. I am not a doctor. But I have suffered for years from food anxiety and seen specialists for it. You are obsessing over this concept of large food portions, and I think your anxiety and OCD are bouncing off of each other. It may, at this point, be something your brain clings to whenever you view this big piece of chicken for example. So many times you've seen an overwhelming portion, your brain has this automatic reaction.

What I would suggest is making yourself smaller portions, and ordering smaller portions. Instead of the adult plate, perhaps you need the child's plate. When you receive that big cut of chicken, break it down. Cut it and determine, this is what I will eat now. And this is what I will eat later. But I will eat it, because I've spent money on it, it has been prepared, and it will feed me essential calories my body needs to function. I know it's hard but try to retrain your brain to think of new thoughts. See the portion in new ways. Perhaps this leftover will need to be divided into two, perhaps you don't need the entire thing at the moment. There's nothing wrong with having a little chicken, waiting thirty minutes, then having a little more chicken.

And, if it's about feeling like you're eating too much, just be realistic and knowledgeable about the calories your food contain. Read the nutrition facts. Do research when you go out. Simply knowing off the top of your head how many calories are in a chicken breast might give you some reassurance.

Hope this helps!