nervous!!!

Hi ladies!!! I just started using this app to track my periods since my boyfriend and I want to start trying for a baby once he gets back from army training. He leaves May 24th and is gone for 6 months. I've been 3 days late on my period and today will be 4 days. So I decided to take a pregnancy test. I'm freaking out a bit. I still need to take the second test. How likely is it a false positive?