Period log

Okay so I've been on glow for almost a month and it said I was supposed to start my period the 20th but I didn't so I've just been adjusting the log everyday to another day behind.. I also have been using a different period log for 2 years now and it says I should have started yesterday! But didn't! Do you guys just leave glow at what it says or let it pass by?? Confused on what to do!