the best thing to do if you want to bend composite decking,,,, cut it to the appropriate size then heat it for about 10 minutes (could take up to 30 if its a 4x piece). Youll need a long tube and a heater,, propane or electical put the deck piece inside the tube (a concrete tube works good just make sure to put something in the bottom so the plank lays flat,and wont warp in the middle, and then put the heater at the mouth of the tube to warm the decking piece.. pull it out screw it into place (do not screw it all the way down as the decking will expand when it is cooled) and then finish screwing down when it has cooled completly.