5 week ultrasound empty sac?

Hello. Wondering if anyone has experience with getting an early abdominal ultrasound and only seeing an empty gestational sac but then having a successful pregnancy? I thought I would have been 5 weeks and 3 days based on conception (there was only one time I could have conceived) but the radiologist said it measured less than 5 weeks and was empty. Could this be because it was done abdominally? Because she also said she didn’t see my right ovary at all yet I know I have both from previous ultrasounds in my last pregnancy. Is it just too early? Should I be worried? I’ve had 2 early miscarriages before and my third pregnancy was my only successful one so far.