I was told I can't change my order

I just bought food at kfc 3 snack burgers, 1street wise 2, crunch burger, 3 small chips, small pops and zinger wings to my surprise the 2 chips we not included I wanted to change my order to family treat and I was toldI can't, im shocked becauseits not like the food is prepared only on request, I was unhappy when I left there is no fast food or retail shop that can't do returns or exchange its not like I took my order outside then returned it. I know kfc won't respond as usual but people should know how they treat their customers. The manager in marlboro is useless.