is my ultrasound normal?

went to get an ultrasound yesterday and doctor told me I might be having a start of a miscarriage or twins. one ultrasound photo had 2 rings (not shown) but it kept appearing and disappearing! they thought I was 8 weeks seeing how my last period was March 13 but doctor had measured and told me I was only 5 weeks and 6 days. she also said that she was not able to detect a heartbeat. should I be nervous or will my dr have a chance in finding a heartbeat next week? also, my ultrasound pic now does not look normal?! what do you ladies think?