Hi mama! Honestly, sa 20 weeks ultrasound ang accuracy is usually pretty high na, like 95% or more, pero may slight chance talaga na mabasa wrong, especially kung mahirap makita ang baby's position or kung maaga pa lang ang gender development. A few of us had to go back for confirmation ultrasounds kasi ang tech said "girl" pero turned out boy, or vice versa, so hindi ko masasabi na 100% guaranteed talaga, but the chances are really good na! Congrats on your little girl, sana matama na ang result!