15dpo faint line or evap

I took this test this morning, I should be at 15Dpo. To me it was a pretty clear positive. I feel I see some color in the line, but I wanted to take another test just to be sure, I didn’t save my pee from the first test so I squeezed out a few drops, just enough to coat the top of the second test, the second test was completely negative.

So could this test be a false positive? Or did I just not have enough to take the second test accurately? Has anybody seen this dark evaporation line?