How to make Glow more accurate?

Melissa

So I get my period VERY regularly - every 28days. However every time glow predicts it, it predicts it every 30 days and it’s super annoying. I’ve already changed my settings so that my cycle is 28 days and that my period is regular, but every month i go to look at my prediction it’s always inaccurate, so I always get my period 2 days before the predicted 30 day mark. UGHH!! Can someone help me please? I know this must affect my ovulation date too.