I’ve had false positives on these too - but also a positive that looked like that. I would agree with above and get a pink dye one - there are cheapy ones in b and m and they are much clearer!
If it’s out of the time frame it’s invalid, think half an hour later is too long xx
Looks like evaporated line but take another one tomorrow or something
I’d get a pink dye test. Found these to show false results x