Thats too funny. I thought exactly the same thing...my Isaac will make some girl very happy in his future lol! But seriously, its put doubt in my mind too. I have no idea about the erection theory..maybe ?
I would be so upset to be told one gender and have another. A good friend of mine was told girl with her first and they went ALL out on the pink stuff, her baby shower was pink themed, pink clothes, she decorated her nursery...the whole nine yards and out popped a BOY!!!. She was a little upset but they repainted the room and kept all the stuff incase she had a girl later on....nope..another boy and she had complications 2nd time around so shes calling it a day and is done. I can't help but feel for her and obviously you've been in the same boat...it would disappointing!
Good Luck on the 18th...I really hope the bub behaves and you'll know for certain....u never know...you could hear Autumn is on her way after all :)