Confused about Glow Prediction

Courtney • Blessed with a rainbow on 11/27/15 💕🎀
AF was 4 days late this month according to glow, so I changed the dates of my period and now it only gives me 2 "fertile days" and they are the 2 days directly after my period is suppose to end. Could that be right or is it a glitch? I am so confused