Do you think my due date could be correct?

Supposedly my due date is 12/8 or 12/9. I am supposed to be 3 weeks today. I found out I was pregnant a WEEK ago tomorrow. So I would have been 2 weeks pregnant. How can you even get a positive that early? I got my hcg checked today and I don’t feel it has cleared anything up for me because it could definitely fit in the 2-3 or 3-4 week ranges 😂

I am not booked for an ultrasound until May!

This is my timeline:

Period- 3/4-3/7 (a little shorter than usual. The period my cycle before was 6 days)

Sex- 3/10 or 3/11

Positive hcg- 3/19

Update: I ended up having an ectopic pregnancy. They had to take out my right fallopian tube and couldn’t believe I wasn’t in more pain