said - then turned +

Ok, my next period isn't due for 13 days so I know I tested early I just have a feeling. But when I took the test it came up negative and I just left it on the back of the toilet and went on about my day. That was about 4 hours ago and when I looked again there was a faint positive line. I didn't wait the full 10 minutes before putting the test down for so long but is it possible this is accurate?