hey, thanks for the warning. Two weeks is a pretty big gap!
In our case the discrepancy was only of two days, and brings it more in line with what we thought. We knew the conception date within a three day range (we "tried" over the three days after I saw the line on the ovulation surge test). Since the surge comes before the actual ovulation, it's more likely the conception happened a two days after it, rather than on the first day we tried - which is what the scans suggest.