US at 6wk and heartbeat was 80bpm anyone else

S • 2 mc then had my dtr 7 yr ago now preg w our second:) happy happy
So i had my US mon at 6wk 2d and heartbeat was 80 doctor said that was fine bc baby HB had prob just started and it will get stronger!!! But from what i read online 80 is low, now I'm worried!!!!