Happy, nervous, and concerned

Hey everyone... Today I had an incomplete anatomy scan but great news, I found out that I'm having a baby boy and I'm so excited! But this incomplete anatomy scan left me with so much concern. The u/s tech was so fake and clearly in a rush. Going by my lmp my due date I'm 18w6d, I found out that I'm a day behind. Okay no biggy. My baby is 9oz with bpm of 147. Almost 2 weeks ago the bpm was 150. My main concern is that the u/s tech kept saying my baby is so small and she couldn't get all of the measurements she needed so they're sending my u/s in for review and on top of that for my next doc appointment (2 weeks from now) I'm having another u/s before meeting with my midwife. So I'm just a little nervous and just want to know if this happened to anyone else? The only test I took was the afp test and that came back negative... I just know that this is going to be the longest 2 weeks ever. Does anyone have an idea on why an ultrasound have to get sent in for a review?