HCG Levels vs Ultrasound

Ke

I went in for what I thought was my 8 week ultrasound last week, but I was only showing 5 weeks. However, they took my blood Thursday and my HCG levels were 33,848 and progesterone 14. I really find it hard to believe my dates were off as I got a positive test on 5/27. Has anyone experienced ultrasound showing lower weeks but bloodwork lining up positively? (I’m still waiting for results from Saturday which was 48 hours after)