Help - question !

Ma
I went in today to see if I could get an ultrasound because I had a missed miscarriage 4 months ago. When we went in the said due to my LMP I would be about 7 weeks but the sac was too small to tell so told me to come back in 2 weeks. I'm worried that having an ultrasound will cause difficulties or another mc because I had it so early? Is this true?