U/sound scn accuracy and fundal height?

You concerend about a 3 day difference? You are at a stage right now that this baby could come at anytime. An ultrasound is just a guess, 2 weeks either way about when you would have this baby. Also you can measure farthur along if you have a bigger baby and vise versa, you can measure not as far if the baby is smaller. I would just be happy that within a few weeks you get to meet your new lil someone and not worry about when.