Cycle Length Incorrect?

Ashleigh • Gave birth to my first on 2/21/15. Lincoln James. 💙
Glow is saying my cycles are 29 days when they are actually 28 days and both cycles I've been on Glow have been 28 days (and I entered 28 days when I initially set up the app). 
​This is throwing off my predicted periods and fertile weeks by a day or so and I can't figure out how to fix it or why Glow would assume my cycle is 29 days. 
​Help!