Natural miscarriage

I'm am suppose to be 9 weeks and went to my ultrasound yesterday and still measuring 6 weeks and no heart beat. The doctor said he saw some blood moving down and gave me the option to either have a natural miscarriage or D&C. I would like to do it naturally but my question is, how long does it usually take? I haven't had any spotting yet. Is there anything you can do to speed the process up? I just want to be done and move on :(