6 week ultrasound

I had my six week ultrasound and they found the baby and heart beat without issue. However, the heart rate was only 90 bpm. The tech said this was not unusual in 6 week tests. Then the nurse called today talking about how my blood levels needed to be taken because I might be miscarrying. Needless to say I was in tears and terrified by the end of the call. I looked it up and many sites say that yes 90 is the low end of normal but it is still normal. I also tested again today and got my 3+. So now I'm just scared.