How about I send my food delivery back?
Why would you send it back?
No, I just feel I can't eat more.
If there were really something wrong, then it'd be okay to send it back. But it's not polite and it's disgusting to send it back just because your full. It's insulting to the workers, and wasteful when you can just get a carry out box.
What do you care about what I do with my food?
Because it is rude to send it back. It is not good to be so picky about your food or the quantity you are served. People won't want to go out to eat with you.