False Positive pregnancy test?

I took an EPT pregnancy test last night and left it in my bathroom while I took a quick shower. When I got out of the shower, I checked it and it said negative, so I put the cap on and stashed it. The next morning I woke up to go to the bathroom and looked at it and it said positive...the line is as dark as the initial negative sign but it is really thin...could this be because the test sat so long? Is this a false positive?