Help! Clearblue digital ovulation test. Got a positive at 3pm but negative at 9pm??

I am using Clearblue digital ovulation test (smiley or empty circle). I'm on CD20 and have gotten all negatives. Last night 6pm got a neg., tonight at 3pm got a smiley! I tested again at 9:30 just to be sure, and got a negative. Did I miss my window, can I still get pregnant? On the strip there are two lines one dark and one a little lighter, not sure if this means anything. 

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