Different dating dates

I went in for my 1st ultra sound today LMP saying I should be 8 weeks but the tech measured me 3 time and gave me 3 different dates. The first u could bearly see baby and she got 6weeks 6 days second one she measured was 7 weeks 1 days and then the last one u could see baby super clearly measured 7 weeks 5 days. And she listed I was 7 weeks 1 day…I’m so confused cause Ik I should be 7weeks 5 days cause I ovulate 3 days late off my period app so since that was the best measure and accurate to my date why did she put 7 weeks 1 day?? She also said I have a little space of blood (can’t remember what it’s called) and I’ll need to come back in a week to get it checked. And I’m worried I’ve had previous miscarriages. Has anyone else had them give u weird dates and the blood pocket and everything be fine?!