Miscarriage question

Hi all I misscarried my baby 11 days ago. I was supposed to be 12 weeks but baby was measuring at 8 weeks. I naturally misscarried and am now just spotting slightly. How long does it take to get a negative pregnancy test. We would  like  to ttc as soon as possible.  I took a test today and did not expecting to be so dark especially since i have no more pregnancy symptoms.