Evap line?!

Okay, so yesterday I took a clearblue test and after 10 minutes, it was negative. So I put in the drawer and left it there for a couple hours. When I went back to go toss it, I noticed it was positive! It was a thick, dark line centered to make a +! I know we should not read a test after, but this is the only test it happened to! Should I just disregard it or could it possibly mean something!? I'm 10 days late and my doc told me to wait another week before scheduling a blood test!