What Causes Negative Scan Results For Pregnancy Despite Being Positive In Tests?

I had the medical abortion pill 9 days ago, I was rescanned and the nurse said she doesn't think she can see a fetus I was 7weeks and 2 days when I had the abortion... My pregnancy test is still saying positive. Me and my partner want to try for another baby but I'm unsure if it's ok to if my pregnancy test is still saying positive even though the nurse couldn't see anything on the scan