I feel like my weeks calendar is wrong on this app, it shows I'm 28 weeks when I'm 29 weeks almost…

I feel like my weeks calendar is wrong on this app, it shows I'm 28 weeks when I'm 29 weeks almost 30. and in the What to expect book, it says I'm in my 2nd trimester and others say I'm in my 3rd. I'm still pregnant, so hey whatever right !