Time scale

Amber

Okay so my first day of last period was May 14th which would make me 19 weeks +1 and I went and got my ultrasound and baby girl was averaging around 18 weeks and 3 days. What does this mean? Does this mean I’m not 19 weeks +1 or is my baby just small. She is sitting verrrryyy low in my pelvis. me and my husband are tiny people ourselves. Just wondering someone else’s intake.