16 weeks haven’t heard heartbeat

16 weeks and haven’t heard my baby’s heart beat. Dr keeps showing me the heart pumping but no sound. Also his ultrasound might be of poor quality because all the sonograms are not clear. All I can see is black and white but can’t tell where the head, legs etc are but he keeps saying “that’s the legs, that’s your baby but I can’t see anything😢 At the last appt I heard to insist that he tells me the CRL and he said that I will find out at my 20 week ultrasound. I don’t know if what he’s doing is correct.