How long for your HCG levels to go down to 0???

How long did it take to get your HCG levels to 0?

It’s been 9 weeks, and I have had a period. However, I got a positive digital and traditional pregnancy test. I had my blood drawn and it says my levels are only 7.7

I was really hoping it was a new pregnancy but I thought it would be a little higher.... I’m thinking it’s probably left over from my miscarriage 9 weeks ago...