Hcg levels after miscarriage

I took Misoprostol last week Monday and Tuesday. I’m not sure if it worked fully...will find out Thursday at my ultrasound appt. I took a pregnancy test tonight to see what my levels were looking like and the test line is still much much darker than the control (on FRER test) like more so than mid to late November when I was still pregnant. Is this a sign the medication did not work or does it just take a while for hcg to go back to zero?