Advice please….measuring behind

I had an early ultrasound sound today at what I thought was 6 weeks 5 days and I measured behind at only 6 weeks, with a heartbeat of 115. I am very confident on my dates, I tracked with opk’s and confirmed with temping, we only baby danced 2 times that cycle…I go back next week for another ultrasounds. Is this bad news? Has this happened to anyone? Would love all experiences, good or bad.