Lines when using an app to invert

Sorry not sure if that’s what it is called, but when you use the app that inverts the pregnancy test. Is seeing a dark line normal without being pregnant? I could be imagining things but feel there is a dark line there but not sure if it is just there because of the invert and where it should be if it was positive and also therefore be blueish in colour not dark. I don’t think I can see it on any of the others and neither on the test as normal. Could just be my wishful eyes. Will check again in a couple of days as still early. Just curious!