Uy, I get why you're worried, pero honestly ganyan talaga minsan ang ultrasound readings, they can vary between appointments, lalo na sa third trimester, so kung sabi ng sonologist normal lang yan, it's likely okay na! A few of us moms experienced the same thing and our doctors explained na less accurate ang dating sa later pregnancy compared sa first trimester scan, so that 36 weeks from your first ultrasound is probably your more accurate due date. But para ma-ease your mind talaga, just bring this up sa OB mo next check-up para ma-confirm siya directly, mas comfortable ka naman talaga if it comes from your doctor, di ba? You're doing great, first-time mama!