I don’t know how many weeks I am?

I’m so confused! 3 days ago I found out I’m pregnant 🎉 yay! Today I had a blood test and the results came back this afternoon, and apparently my HCG levels were 45 which shows I’m “only about a week pregnant” according to the nurse I spoke to... however according to my last period I’m nearly 5 weeks.. I don’t know which result to go off?

What result would you go off? 😅