Does anyone know how accurate the measurement of the babies weight is on the ultrasound compared to what it's really weighing at that time?

I just had an ultrasound, I'm supposed to be 30 weeks 2 days. And at the end of the ultrasound, the tech pulled up the report and it said I'm measuring 34 weeks and the baby is weighing in at 5lb4oz.

Could that number be off by a pound or so?

Could I possibly go into labor sooner than I think?

Or should I just prepare myself for a really big baby? Lol