36weeks + 3 baby didnt gain weight from previous scan

Ultrasound scan might be inaccurate (plus minus 10%) so it might be due to that. Don't worry too much, the detailed scans should give a more accurate number. In my case my baby's weight really did stagnate so she came out at 2kg but otherwise totally fine. She's 2.5 years old now, healthy and active. I hope that gives you some assurance!