Measuring behind? Stressed out

Anon
So basically I'm 33 weeks and 1 day and my belly measured 30cm I just got an ultrasound 2 weeks ago and baby was in the 34 percentile and weighed about 3.5lbs the ultrasound tech and midwife said shes small but still in the normal percentile and not to worry everything looked fine. Well when I went today my doctor said I'm measuring small still and she wants to do another ultrasound in two weeks to check on the baby again and not to worry that she just wants to make sure theres no growth problems well i can't help but to worry bc if she measured fine last ultrasound and she looked good then why do i have to get another ultrasound 😓😓 she also said she isnt worried and I'm just really small and probably wont have a big baby or anything. I just am trying not to worry.