Hi Stephanie! There have been a lot of great comments, but let me try to focus on the point you are trying to discuss.
A number of years ago my wife and Tina were going to spend a day together and by the time Tina got finished with the makeup and the hair and the clothes and the heels, well, she felt terrific! She started to walk through the bedroom and felt that she had really hit it that day...until she walked by a full-length mirror and saw the combined effect. She was shocked!!!! The little details had worked well, but she hadn't yet let herself go to be a girl. Frankly, as she stood there, she looked like a guy Marine dressed as a girl (well-dressed, I might add ).
I related that shock to my wife and we started a discussion about gender clues that we all give off. What do people recognize instinctively as a smile of a guy vs. a smile of a girl? How do we stand to signal "girl" and not "guy"? What should we do with our arms to signal "girl"? That general area called "deportment" is really tough, especially in 4" heels. That first discussion with my wife started months of her pointing out women and how they acted different from men, often in very subtle ways. I think that's what wbdavid meant in her post, saying that you looked like you were born a male.
However, even if you had perfected your girly smile, had done something different with your right arm and had pointed one toe out a bit, there still can be so many more male clues, and you can't hide them all. Everyone here is right when they say that passing is mostly mental, and won't happen all the time. There will always be a few male "clues", and if someone is tuned into them (as we are), they will always give us away. We simply have to accept that and move on. The more we dress, the better it gets. Remember that women have a whole childhood to practice 24 hours a day! We just aren't going to attain that kind of perfection in a few hours a month, and we have a bigger mountain to climb since we start with male bodies!
We can only do our best, practice, practice, practice, and have fun! One great thing is that we have 3 billion role models on the planet!