thanx Les! that works fine !
my code line is now:
$oXL.ActiveSheet.PageSetup.Zoom = Not 1
$oXL.ActiveSheet.PageSetup.FitToPagesWide = 1
$oXL.ActiveSheet.PageSetup.FitToPagesTall = 50

(i am using 50 because i don`t know on runtime how many pages my excel sheet will create, but i like all the pages to be exactly 1 page wide)