Belly Measuring Small 35 Weeks

Anyone have any experiences with belly measuring small for gestation after 35 weeks? Had an ultrasound about a month ago and baby was 18th percentile. At my appointment yesterday my belly measured small (he didn’t tell me how small) and now I’m having another ultrasound tomorrow to check growth. I wasn’t too worried yesterday, but today I’m feeling a little anxious. I’ve had 4 miscarriages in the past so it feels like I let my guard down once I got to 20 weeks and now something bad could happen. Baby’s heartbeat has been good, he’s moving like normal, I’ve gained 30 lbs so far, BP has been perfect, no GD so I don’t really know what went wrong in the last few weeks.

Note: not my first take home baby. He has a 5 year old sister who was born healthy 6lbs 15oz at 38+3.