there is no built in way to align strings. Try this method from my BlitzMax Framework:
Function ccDrawTextCentred(text$,x#,y#)
Local w# = TextWidth(text)
DrawText(text,x-(w/2),y)
End Function
Function ccDrawTextCentred(text$,x#,y#)
Local w# = TextWidth(text)
DrawText(text,x-(w/2),y)
End Function