I think I agree with Lori Ann. If unsure, just drop the gender address (sir, miss, etc.) entirely.
But - without seeing what the OP looked like at the time, I'm guessing that the greeter's quick glance saw what looked like a male to her, and she just automatically said the "standard" phrase... probably without a second thought. She was most likely looking to whoever was next and repeating the same thing.
Personally, I'd say "shrug it off and move on." I doubt the poor girl meant anything by it.
