It'll fit. The legs that go into the end don't have to go in the same amount. So as the back of the trigon is a 90 degree corner, you can get each of the legs to be at 45 degrees by having the rear legs in further than the front legs, angling the 'feet' at 45 degrees. You'll need some self adhesive velcro to stop it being pushed back (if feet are on the outside of the pelmet) or forward (if feet are on the inside of the pelmet) and dropping down.
That's if hanging it with a hanging kit isn't possible.