How could I be so far off?

Alicia
Went to the Obgyn today and had my first ultrasound and found out that I was off by a whole 2 weeks. So I am only 6 weeks and 1 day instead of 7 weeks 5 days That would mean I got a positive pregnancy result only being about 4 days pregnant is that even possible? Or could there be something wrong that would cause my baby to be smaller already?