If ultrasound said the baby is a boy, and the outcome is girl, that means the technique of the one doing ultrasound is poor..
Ultrasound is "operator-dependent", i.e. result depends on how you do the ultrasound
Don't worry wow. Try try 4D la. My daughter was confirmed as a girl in Tsan Yuk Hospital. The doctor also taught me how to see tim! But he's the lecturer of medical department in HKU.