Do I Trust My Body or My Cycle Calendar for Fertility?

My period is very regular and I have been using "natural family planning" as a form of birth control. Basically, I use my discharge as an indicator to when I am ovulating and I refrain from unrpotected sex when it is clear and thin. My signal that I am no longer in my peak fertility is when my discharge goes back to thick/white/chalky. Tell me if I have this wrong, but this is the method I have been using for a while now and I have not gotten pregnant.

Anyways, last night I had unprotected sex with my partner and he finished inside of me. My discharge throughout the day was white and chalky so I assumed I was in the clear but when I looked at my period calendar, it said I was in peak fertility.

Should I trust my body signs or the app calendar?? I am not sure if I should be worried about pregnancy or not.