Plane mad Harry

Hi, I've recently purchased a large STI style boot spoiler for my 2002 bugeye WRX, I have had a spell in hospital so have only just got round to fitting it and when I did fit it I noticed that it would move a bit on the boot, I noticed that the skin of the boot the spoiler was bolted to was flexing and this was causing the spoiler to act as though it was loose, any ideas on how to fix this problem and is there anybody out there who as had the same problem, thanks from a very frustrated Subaru owner. Help Help Help !!!!!