First time using ovulation tests! HELP!!😫

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According to Glow I'm in my fertile window and should ovulate on the 20th. I know this is just an estimate so I've been checking CM and testing 2xdaily but getting negative tests, not even a faint line to indicate there's any LH in my urine whatsoever.
How close to ovulation should I start seeing at least a faint line? I'm just worried that I'm not going to ovulate, I'm CD12.
If anyone can give me a little advice that'd be great. 😘