I’m confused.

Today I had an early ultrasound at 6+2. They could only see a yolk sac and a fetal pole. Not much baby. Which is fine, and expected. I go back in in a week. But what I’m confused about is that they told me I’m measuring at 6+2, right where I should be. If that’s the case, why can’t they see more? Why do other people see more and measure the same? They can even see heartbeats. . She said her machine was new as well. If I’m measuring at 6+2 and another woman is measuring at 6+2, shouldn’t we be able to see similar images? What am I missing?