Thought I was 10 week but baby measuring 9


Went for our first private ultrasound Sunday and according to my last period and my app and midwife I should be about 10 weeks two days today. When we went to scan they said baby was measuring 9 weeks. Does baby look like its 9 weeks or 10? And Has anyone else had baby measure behind predicted date then the first dating been correct. Really confused as I thought we were further along.