Hai! Honestly, ultrasound around 18-20 weeks is quite reliable untuk determine baby boy, tapi ada still small chance of error especially if baby position susah atau scanner quality tertentu jer, a few of my mum friends got "confirmed boy" tapi turned out girl last minute! Best thing is confirm dengan your doctor dulu, sebab they can give you proper confidence level based on what they saw. Congrats on your first baby though!