Using Glow Percentages to TTC

Hi ladies!
I am loving Glow so far. It's so easy to use and helps me keep monitoring my body a top priority. 
I am in need of some clarification though. When the app gives you a percent age chance of pregnancy, does that mean that my bf and I have to TTC on that day? Also, the highest percentage I seem to be getting is 20.2%. But, I notice that some women on here have percentages as high as 38%. Does anyone have any insight on why my percentage stays so low? Thank you and good luck to all of you future mommies!