Low lying placenta


I was told I had a low lying placenta at my 19/20 week scan but they said it could move. Went today for my 28week growth scan as my little man has a duplex kidney on the left side. Well it hasn't moved so I go back for another scan in 3weeks and if it hasn't moved I will be having a c-section done. Has anyone had this and it still moves after 28weeks?