Are my OPK's wrong?

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Hi everyone, I'm starting to get a bit confused with my ovulation predictor kits so hopefully someone has some advice!! 
According to Glow and Free <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Menstrual Calendar</a>, I should be in my fertile week right now with ovulation Friday (31 July). I have definite EWCM since today, and am literally wanting to leave work early to DTD lol - basically I definitely feel like I'm about to ovulate.
As recommended by my OPK instructions, I started testing a few days ago but the results are confusing, as the line is getting lighter instead of darker. Are the tests wrong or is this suggesting that I won't ovulate this month!? 😳
I'm using kits off Amazon that had lots of good reviews.
Any thoughts?!
Thank you!!