I havn't used home pregnancy tests before (And never been pregnant before, other than hopefully right now LOL) but I dont have much faith in them. So many of my relatives have told me how inaccurate that are- some say pos and they are wrong, and most say neg and they are wrong (In the instances with those I have talked to) In my opinion, if one minute one can say neg, and the next it is pos and the next it is neg- I would be pulling my hair out!! Lol.
So I would say yes- you still have a chance that you could be pregnant- especially if AF still is not here. Maybe wait a few days to see if AF shows up and if not, go get a blood test done to be sure- less stress is the best!

When my AF is due and it is my turn to take the test, I will just be going to the doctor and getting a blood test as I am sure they are more accurate.