Confused about weeks pregnant..help

So maybe I'm just missing something. I know that technically a pregnancy is 38 weeks but they make it 40 and go by the date of your lmp. What I don't understand though. When they say "this is my 4 weeks scan" is that actually 4 weeks you've been pregnant so 6 weeks by the add two weeks convention? Or actually 4 weeks so two weeks after conception? I'm previously had a miscarriage and a neuro issue makes me high risk. I am getting an early us tomorrow but idk what to expect. My lmp was May 2nd so by their method I am 5 weeks and some days pregnant.. But I have a long cycle and I think I ovulated on May 24th.. So by actual conception date I am really only 2 weeks.. Or 4 weeks if you add two? Really confused and wanting to know what to expect..