Period on app

Kelsey • ICU Nurse 👩‍⚕️ Baby Girl: Miss Maggie “Mermaid” 🧜🏻‍♀️🧜🏻‍♀️ 11/24/19

So my period is predicted to start today but hasn’t yet but my app is automatically saying I started it. I clicked to edit it to remove it. But now it has said predicted start date is tomorrow??? Super confused! Also how do some people get it to say period late??