1 cm dilated! Ultrasound says he could be 8.5 lbs!? how accurate was your ultrasound vs actual birth weight.

Crystal
Just found out yesterday I am 1 cm dilated! According to his measurements I am 39.5 weeks pregnant and he should be here Thursday! We know our date of conception though and technically I would deliver the 21st. Also his ultrasound shows he weighs 8.5 lbs!!!!! Is this accurate!?Thoughts and opinions?