I agree that we all were never girls. We were females simply because our bodies are/were female. Those bloody xx chromosomes made sure of that. But the word girl is a social and cultural concept, and that's something we never were, or are.
That being said, I don't miss anything of being perceived female. But there was one thing that was a bit of a perk (as in, it was the only positive thing about it, but I don't miss it). As a perceived girl in the gamer community, I was a tough, cool gamer 'chick' (geesh, I hate that word. Why are girls compared to baby chickens? Fluffiness? Cuteness? They both peck?). Now I went from cool gamer girl to a nerdy, standard nerd. Not a loss I miss, but still mentionable.