I don't think 600 calories is a lot for 4 weeks out. I think that 500-800 range is a sweet spot for most people, actually, so I think you are good there.
You will learn what feels right for you. I am 40 days post op and for me 800 is very very comfortable. More than likely you were just fne the way you were, I wouldn't feel like you need to stuff yourself because of what other people think.