Scan today - gestational age seems off

I didn’t have a menstrual period last month as I had a chemical pregnancy. I got a smiley on ovulation around 12th July and did BD on 12 and 14th.

I expected to be around 6 weeks 4/5 days possibly had a positive test on 23rd July . The scan today saw a gestational sac, yolk sac and heart beat. Measuring at 3.4mm but when they calculated age they said 5 weeks and 4 days 🤷🏻‍♀️ . Doesn’t seem right they said as I’ve not got a LMP to go by they go by the ultra sound.

Thoughts? Scan is below