Baby gender? not sure if its a boy or girl? help!?

Today I had a sonogram, I am 17 weeks 6 days, the baby was very active and we were hoping to find out the gender. The baby would not open its legs but the ultrasoound tech said she thought it was a girl bc it didn't have boy parts sticking out. My question is has anyone experienced this and later found out the tech was wrong with their predictions?... I am not going to tell anyone the gender until we. Were 100% sure.