This app is saying 38 weeks while my scan is showing 39 weeks🤦‍♀️

Ocho❤️

This app is saying 38 weeks while my scan is showing 39 weeks🤦‍♀️.. can someone explain this to me please? And I’ve having constant cramps.. my feet hurts, I can’t even get out of the bed without feeling pains in my lower abdomen and my private part😫😫