Glow predicts me to ovulate in 3 days??

However, I done a test today and I know it’s not positive but does it look to dark to ovulate in 3 days?? I was thinking maybe tomorrow or the next day? But I don’t know hoping someone can help as I’m new to all this?? I’m on cycle day 15 now, grow predicts me to ovulate in cycle day 18, as my cycles are around 31 days? Thanks in advance x