Boy or Girl??

Everyone keeps telling me that the odds are against me to have a boy. Supposedly the theory is that once you have 2 of the same sex that your chances of having a third of that same sex are much higher. Is this just something that someone made up along the way or is it really true?? My curiosity got me so I researched it a bit.

The Odds of Having a Boy or a Girl
The usual pattern of births is 51%boys, 49% girls.
If the first two are boys -- Odds are 53.3% the third will be a boy, vs 46.7% it will be a girl
If the first two are girls -- Odds are 54.0% the third will be a girl, vs 46.0% it will be a boy
*so because I already have 2 girls, I am more likely to have a third girl... but only 4% more than 50/50. Sounds like pretty fair odds to me.
I got this info from http://www.in-gender.com/XYU/Odds/Gender_Odds.aspx.

With that being said... I have no clue what I'm having. Another funny question... are you going to let it be a surprise? Well, yes, It will be a surprise when I go to my appointment to have an ultrasound and they say.... it's a______!!! It's just an early surprise. :-)Here I am at 19 weeks pregnant. I'm dreading gaining weight everyday for the next 5 months. It just sucks. I've never had that feeling in the past (maybe that means it's a boy) :-) I guess it's because I just finished losing the weight from Avery and now it's time to pack it all back on. UGH!