I haven't replaced my headlights but bought the truck second hand and my filler pieces stick out a bit on the outside corners of the headlight, where it bends toward the reflector. I'd love the suggestions too.
Also kitch, depending on what year your T is. Be careful with them. mine is an '06 and the parts that hold the clips/ pins are extremely brittle.
All headlight years are the same assembly, just the older ones have the clear parking light lens. Don't know why the trim piece wouldn't fit in it. I know they're dumb questions, but are you sure you're using the correct side for headlight and trim? Just trying to narrow it down. Pictures of how it doesn't fit would help.