How do you get glow correct

Christin • Wife & Mother. Ttc 2 ♥️ law
My ovulation predictor is off by just a few days. Says yesterday was my highest day but I know it won't be highest day until a few more days. I keep logging in that there isn't a positive lh surge and my periods are right I even switched it to 29 day cycle
How can I fix this?? I ovulate on cd 15/16 so about 3 more days