Trigger shots

This is my first round of trigger shots and needed some clarification on how this works. So once you use the shot then afterwards get the iui if you test too early you will get a false positive right?? So in the first picture I had the trigger shot the 19th and iui scheduled for the 21st. I am currently in my 2ww but I cant stop thinking and wanting to test. So today I took a test and it had a very faint line(the second picture) could this be a positive test or am I still cutting it too close to the time that I used the trigger shot? And what exactly happens if you take the test too early? So it’s dark then gradually it lightens and if it’s positive after the shot is out then it goes back dark again??