No test line on OPK

Breanna • little man born 02/2019 💙

According to Glow I should be ovulating on the 1st, but the OPK I took yesterday and today both have a totally absent test line. Brand is First Response. Should I be worried it's not happening? Is it possible I just ovulate later than Glow predicts? I have a fairly regular 28-30 day cycle...