For 99p, I'd be chopping it up! Maybe take a bit of the height out of it and try profiling it to the tailgate. Then if it still doesn't look right you've lost a whopping 99p. Failing that, drive to your nearest Maccy D's, find a kid in a Saxo, sell to him for £100 telling him it will give him 50BHP downforce factor G4.5 and he'll tear your your arm off
I too have a huge spoiler, but luckily I know what it looks like finished and fitted so no surprises when it comes back from the bodyshop.