If it doesn't sit flush without coercion, I will be returning it. No way am I monkeyin' about with it. It fits or it don't (and gets returned).

 

I used silicone in conjunction with the 3m tape for my large trunk spoiler, and I had the same problem with the ends popping up. Based on some advice I received from CJITTY, I reheated the silicone at the corners, added some more silicone, and then I used some heay duty plastic clamps to hold the corners to a small section of the trunk lid.

 

Got mine done today. Took lots of pics and will post a short DIY. My spoiler fit nicely and did not require much coercion at all. My only complaint is that now my trunk does not full pop open anymore. I will have to do some modifications to make that happen....stiffer torion bars, or......