baby measuring

I’m 34 weeks today, I’ve been going through syncope episodes since February, I’m only 17 so I’m tiny as is, and I had my OB appointment this morning, I’ve only had my cervix checked once around 13weeks due to switching doctors and only one ultrasound which was 23weeks and she measured at 22weeks and 4days when I found out it’s a girl. My baby girl is measuring at 30weeks today, and I’m 0.5cm dilated . I have an ultrasound scheduled before my next OB appointment to see what she’s actually measuring but has anyone experienced this? I don’t want to be panicking..