6w HR??

MB
So I had an ultrasound today and I was "supposed" to be 7w but they got me at 6w with a HR of 116. I didn't have this with my first, we saw a fetal pole at 5w and then went back at 7w5d and got a hr of 155. Dr said no reason for concern, everything seems fine but I go back in 2w to make sure we're progressing. Stressing a bit! Anyone else get low hr for 6w and it was all okay??