7w4d heard heartbeat

Katie
Hello! 
I had a scan this morning -- a few days b4 they wanted ;) started to not feel pregnant and needed that re assurance. It's my first pregnancy via ivf-- due 12/30. 
At first they thought it was measuring a few days behind which really freaked me out-- but she kept re measuring /getting it in right spot and finally measured at 7w4d. My last scan I was one day behind -- anyone else measure a day or so behind ? 
Also-- heard the heartbeat phew. 161 beats per minute my nurse practitioner said that was great, nice strong heart beat. That sound right? I know it's suppose to be super fast but that sounds fast ha!🙏🏻❤️💆🏻