Which twin is Which?

I was in a shop yesterday buying grass seeds for my front lawn, when someone I vaguely recognised walked by. She walked by at least two more times before finally stopping and asking me how I was doing.

Then I remembered! I knew this girl from school, eight years had passed since we last saw one another.

So we spoke for ten minutes, then we said our goodbyes and see you soons and continued on our merry way. Only thing is, this girl is an identical twin. I had no idea who I was talking to, and she had no idea that I had no idea.

Awkward!