you can lay the chassis on the sheet before you take the film off of it's protective backing and then you can mark cutouts for the film. Then before you take the film off the backing, you can cut it out like you would mask from a body, then you would weed out the uneeded sections, peel it off the backing, spray some windex on the chassis and on the film, and then slide it around untill you get the perfect fit. I you allready applied the film, well, you're SOL for advice from me. Sorry.
Hope this helps.