Pregnancy test advice!

I took a test the other day and it appeared to be a BFN. I decided to test again today since my period is due in two days, when I went to grab a new test I saw the one I had taken a couple days ago and it seems to have a very faint line. I used a pregnancy test checker app that inverted and changed it to black and white and there's definitely a line there. But could it actually be a positive result or just from sitting there a couple days??