when should you test negative after miscarriage

So my DR told me to test for HCG a week after my miscarriage on the 26th and it should be negative so I test again today as I wanna TTC again asap and this is what I get why is it still positive shouldn't it be out of my system by now? It's faint so I guess the level is going down but it's been 11 days it should be gone they didn't see anything on the 26th and said I had passed everything they wanted me to test and in a week just to make sure I wasn't so early that couldn't see anything but my test should be getting darker if I hadn't miscarried right so seeing this positive just sorta hurts 😞