Help?

A few weeks ago I had what seemed like a miscarriage at 7 weeks. I passed huge blood clots and tissue. When I got checked before passing the pregnancy tissue, they told me my HCG went from 8800 to 7100 in one day. I read that the hormones are supposed to drop 50% every two days. It's been 16 days and I only bleed for four days total. Last night I wanted to take a test to make sure it was negative which would mean my horomones were back to normal. It still says pregnant. I know it can take some time for levels to cease completely but it's been so long and being that they had dropped so drastically before I'm wondering if i maybe didn't pass all of it although I think I did. I'm quite confused. Has anyone else experienced this?