Was you first u/s 9 weeks by your lmp?? If it was then by their measurement the bub would have only been 3 or 4 weeks when they did the scan so how could they have even given you a date, iykwim??
I think the obs go off the earliest scan for a due date, so that will probably stick, and i have heard of people having higher fundal height than the 'recommended' height, maybe ask for another opinion or something though??