Ovulation test question

I'm new to this whole ttc thing. I know that when you take an ovulation test for an LH surge the line has to be as dark as or darker than the control. But I was wondering if it meant something that a line did show up but just wasn't as dark as the control. This feels like a dumb question but I'm wondering because I just took an ovulation test just to take one and didn't expect to see any kind of line at all because I am 3 whole days away from the beginning of my fertile window according to glow. Last month I took a test when glow said said I would be ovulating and got the LH surge. Does this mean that my ovulation days are changing or is that normal 3 days before my fertile window starts?