My u/s have consistantly showed me to be a week behind my LMP date. My OB wont change my EDD because he said they only do that if its more than a week. If its more than a week the u/s date becomes your new EDD.

Good luck. I'm sure things are fine - its so tricky at the very early stages - so may people have felt doomed like you and 7 or 8 months later are holding their little bundles.