TA ultrasound and TV ultrasound different dating?

So I had a Vaginal ultrasound on Tuesday, and the baby measured 6 weeks, heartbeat of 88, and wasn’t visible on an abdominal ultrasound. Today, 3 days later, they did an abdominal ultrasound, the baby was visible now and the heartbeat was 110, but the baby was measuring 6 weeks still. I’m wondering if it was because of different methods of ultrasound, and the machine was different? The doctor didn’t seem concerned but of course I’m freaking out!

(If you’re wondering why I had two this week, I had two viability ultrasounds to make sure the heartbeat increased.)