If I were a girl from the beginning, I'm pretty sure I would have been at least a little different than I am now, because of my hormones being different.
The levels of estrogen and all that would have at least deviated the way I learned to think things, and my personality by at least 3%.
Also, I would have grown up with different people around me, and different types of thoughts and ways of life would have been forced on me, so that would contribute at least 2%.
Together, I think I would have been at least 5% different from who I am now in terms of thought process and personality.
But, if I was just turned into a girl right now, after being a guy for so many years, and after I have already finished building up the frameworks of my mind, and have finalized my personality and thought process after years of building them, I'm glad to say that other than my appearance, I would have been pretty much the same person. Specially no change in personality would occur for sure.
Socially, it wouldn't put much of an impact, because I have such a personality that I can fit into any of the two genders without anyone pointing out something out of place for me. I would have easily been accepted more into society, as there are some predefined good sides of being a girl.
But then again, I would have become a homosexual person. That would certainly not go unnoticed, lol.
I guess some of my traits might come off as tomboyish, maybe. And a bit of a tomboy personality is even loved by me, so I think I would be accepted as a little different but awesome just for that kind of girl.
Like someone said here, I think it would have been kind of cool to have the ability to flip back and forth between genders, lol.
tl;dr version: I would be the same person, and only my appearance would change.