what is your baby heart rate

So I had a ultrasound today I had a miscarriage 12/6 no period in between my dr said I'm about 6-7 weeks heart rate was 128 bpm dr did not measure fetal pole said it was really tiny but told me that heart rate was a little low curious to know how can she say that is low when we don't even have a accurate date or really no how far I am smh she really has me nervous go back in a week to get a dating scan what was your baby's heart rate between 6-7 weeks