fiber glass they said it came with all the shit to install it . i called to ask (after i paid for it ) how it attatched to the trunk lid . thats when i found out it needed 2x sided tape . so yup its a stick on .
Go to AutoZone, get the biggest roll of 3M 2 sided tape, put solid strips across the spoiler long ways on the trunk flat, curve, and vertical sides, then some on the edges between all them. Then put a few strips between. line it up, pop it on, sit on the warped side for a few mins. and it should be fine.
Seriously though, have you talked to the company that you bought it from? I'd try to make them replace it, if its hollow it probably won't stay down for long. Otherwise, maybe try gluing in some bracing inside of it to give you more rigidity and surface area for sticking.