Need some personal experience stories please!!

Today I went in for my 8 week ultrasound, and got some concerning news. The baby is measuring only 6w6d, and has a heart rate of 85 (I was told it is expected to be over 100). I am kind of freaking out because I have had 5 miscarriages, and I dont think I can bare another one! Im positive of my conception date, but guess it is possible that the little guys partied in there for a few days before they did their business (men 🙄😆) putting me closer to 7 weeks. That doesn't really explain the low heart rate though, does it? Anyone have this happen, and have a positive outcome?