Frustrated

Last period was late May. Which would put me at 13-14 weeks. Went to get an official ultrasound and baby is measuring 9 weeks. Two weeks ago at my first doctors appointment nurse saw the baby and said oh you look about 9 weeks. Two weeks ago how had the baby not grown. Also, never got a period in June, putting me at 9 weeks would mean I got pregnant first week July. So confused and worried baby isn't growing.