Glow was wrong

I've been using glow for sometime now and I've been relying on it for my ovulation days but had no luck, so I decided to purchase my own ovulation tests and according to Glow my peak day is 3/22 but I took my ovulation test this morning and got a positive test. So I'm wondering how accurate this app is even when you record your cycle regularly. I know it's just an app, but I know there are some females who really rely on this app.