There's a reason you were told to wait 2 weeks to come back. If they were certain there was an issue, they wouldn't be having you come back then to look again. Things are sometimes very difficult to determine in the very early weeks after conception.
I am always curious about early pregnancy dating. Did they simply look up your dates by the date of the start of your last period and that was it? Or was there more to it? I ask this as someone who did not have "normal" 28 day cycles. In fact, just before I got pregnant with our 2nd child, my cycles were closer to 40 days. I had one that was 42 days, if I recall correctly. That sort of changes when ovulation occurs (if counting from the first day of your last period). And they sent me over for blood-work at 5 or 6 weeks, thinking I had perhaps had a very early miscarriage when they couldn't find anything on ultrasound (despite no symptoms of miscarriage whatsoever, and the familiar nausea having already set in).
But, using a later conception date than the standard calculations put me right on track. And she just turned 14 last week.
Just try to be patient. Distract yourself with other things if you can. And go back in 2 weeks and see what's what.
Blessings to you.