When you can't finish your meal

What do you do when you can't finish your meal? I prepare an appropriate portion size (about 4 ounces) and eat slowly with small utensils. Sometimes, before I finish the portion of food I prepared, I start to feel full, so I stop eating.

I'm sure this happens to most of us on occasion, so what do you do with the rest of the food? I usually put it in the refrigerator for a while and then go back and get the rest later. I don't know if this is the right approach, or if it's a bad habit that will come back to bite me someday. I'm a little worried because I recently saw a WLS YouTuber say that this is a habit that contributed to her regain.

I don't like wasting food, but I can get over that. The bigger problem for me is that I plan out my meals to get enough protein, and if I don't eat all of what I served myself, I'm going to be short on protein. I'm not eating an excessive amount of food; I rarely go over 600 calories in a day, and I sometimes get full before I finish something like 2.5 ounces of Greek yogurt or a small salad with 1.5 ounces of chicken. Today, I started eating 4 ounces of pureed black bean soup with half a scoop of Genepro, and I felt full after eating about 3/4 of it in 15 minutes. I only eat three meals per day and no snacks other than protein drinks between meals, but I'm afraid that this might be kind of like cheating, because I'm sort of having the rest of my meal as a snack.

I'd love to know how other people handle this situation!