@hamilton,
Was it at the drive-thru? Always check your order at the drive-thru.
In Joe Pesci famous words:
"And I'll give you two guys, a friendly piece of advise, ok? Don't ever go up to the drive-thru, ok? Always walk up to the counter. You know why? Ok, ok, ok, ok. They f- you at the drive-thru, ok? They f- you at the drive-thru. They know you gonna be miles away before you find out you got f-ed, ok? They know you're not gonna turn around and go back. So, they don't care. "