Question

Gabrielle • Married💍, lost our angel 09/02/17👼🏻, Pregnant with rainbow baby 🌈👣

I have this app and I put in my date of last period which was October 4 2017 once I entered that it said I am 4 weeks and 3 days is that correct it says my conception date was October 18th I need some advice the app I'm using is Ovia pregnancy