had my ultrasound today and baby is measuring a week early

I was more than surprised at my appt that my lil one is measuring a week early. He must've hit a growth spurt. Four weeks ago he was only 3lbs 4oz now he's 5lbs 12oz! Nervous that my lil one will be a big one! I'm a FTM and now I worry if I will go early or if he will be a 10lb baby....has other moms experienced this??? 😬