Excel VBA: getting row of clicked button

Try this:

Sub Mainscoresheet() 
     ' Mainlineup Macro
    Dim b As Object, cs As Integer 
    Set b = ActiveSheet.Buttons(Application.Caller) 
    With b.TopLeftCell 
        cs = .Column 
    End With 
    MsgBox "Column Number " & cs 
End Sub 

Each Shape has TopLeftCell property. It contains a cell within which the top left corner of the shape resides.