Tests getting darker. 2 and a half weeks after d and c

So I had a d and c 2 and a half weeks ago and only had sex 4 days ago.

I took a test yesterday to be sure that all the tissue was removed but had a faint positive.

This morning I took one and it's got darker.

Anyone know how this has occurred.

Going to see my Dr Friday to do tests as they could have left tissue behind.