Unsure of how old my little peanut is

Anywho, I went to the doctor after I found out I was pregnant. Like, right away. And thennnnn, i went and they drew my blood and told me to wait some days to tell me an estimate of how old my little peanut is, so they say 2 weeks or maybe even 3, but to wait till my first ultrasound in July for a more accurate number. Then a generator for an expected due date online was based on my last period, which says it's 4 weeks. So I'm not sure. I have a small bump, too. I wasn't even this bloated and bumpish. I have stretch marks, too. But I just would like to know, it's my first pregnancy and I'm curious how far along the growth is. Had this ever happens to you?