Do you have any idea when you ovulated??? This would give you a more accurate EDD. From my LMP, i would be 12+ weeks, but I know when I O'ed, and I am going from that which makes me 8+3 weeks.

Also, your fundal height measurements should give you a better idea of your weeks. Or you could aim for the first date, and be monitored more closely after that day to check for plancental failure, which is pretty rare anyway. remember, pregnancies go 42+ weeks with no problems for the bub....