So confused with dates!!

I wondered if someone could help me please.

My apps all say I’m approx 7weeks 3+ day based on my last period.

I was pregnant in 2019 and went for a private scan thinking I was 7 weeks but they told me I was approx 5 and then a week later I miscarriaged.

I’m not terrified to go and have another and be told I’m less along that I am. Would a scan go by the same approx date or is it measured the same ie date of last period?

So confused and totally projecting on dates xx