No, actually, you weren't first in line.

The husband and a friend and I were in line for something this morning. Along with a few other people, we were to the side of a particular entrance, and there was at least one party behind us. A group of 3 girls came up and decided to "wait in line" as well, though they decided to just wait in the middle as opposed to the side where we were. When the gathering became an actual line, the gathered groups merged, with us in front of the group of 3 girls, but with them in front of the party who had been waiting behind us. They seemed to take exception to that. A few minutes later, one girl very loudly commented to another girl, "Weren't we the first in line?", to which I, probably to her surprise, turned around and said, "No." and then turned back. No further comments from them.

Just because you don't notice or recognize that a line has already formed and you decide to just stake your own claim doesn't in fact make you the start of the line.