Cuppini rear luggage carrier with backrest and handgrips

just bought one of the above ( art number is 75238000 ) for a 2011 px 150 and i cant figure out how to fit it , the  bolts on the scooter are too short which is easily sorted , but it seems to me that when fitted i wont be able to operate the side panel release levers and the bar that runs on the rack the length of the seat will stop the hooks on the side panels engaging if i take the panels off , am i doing something stupidly wrong in the way the carrier is fitted to the scooter , any help please .