Frank & Eve, just for the heck of it I googled up "how to remove stains from 3M clear film", and it looks like your SOL. Even the pro's can't remove a stain that's leached into the film, 3M, Diamondshield, and others. They say that anything strong enough to remove the stain will eat into the film itself.
Going further, removing the film can even damage the paint, and even remove paint depending on how much the paint had "cured" prior to the film install.
You might just have to live with it, and as it's high up on your cap, might not really be that noticable.
Maybe time for a custom "Frank & Eve" vinyl decal to cover it!!!