anyone else?

My daughter was born pretty big- 8Ibs. 9oz 21.5 inches long. Now she's 6 months old weighing in at 20Ibs and 28.5 inches long! She's wearing 6-9 months and almost growing out of them.
I just don't see how she is so chunky when she only eats 26-28oz of formula a day! Sometimes less! I figured she'd slow down in weight, but she isn't at all. 
Should I be concerned that she is so big? FTM here and everyone makes fun of me and her for her being so chunky so it's really getting to me.