Measuring 7 weeks 158 HR

Christina
Went to the hospital today after waking up, still, with brown blood when I wiped. From my last period we assumed id be at 9 weeks, but he did an US and said I'm more like 6 or 7 😳; and said the heart rate was at 158.  Did anyone else measure smaller then they expected? And what was your baby's HR? 
TIA  xox