Installing pet door in fiberglass exterior door?

I've been installing flooring and left a 1/2" gap by the exterior door. However, after I thought maybe the metal trim was supposed to cover it. is there something I can do to cover this or just wood baseboard trim? Doorway trim https://imgur.com/gallery/eCi342T

hi, I'm replacing the side door in my garage. After removing the old door I'm noticing that the bottom of the rough opening is not at all level. I just wanted to float my plan out there to make sure I have the right idea [list] [*]level off the threshold with concrete [*]put down a 1x6 piece of pressure treated lumber [*]then put down the sill tray that came with the door (using the recommended caulk between it and the lumber [/list] If I didn't level off the concrete, I'd end up with about a 1" gap between the PT 1x6 and the concrete. I tried to use a concrete patch product, but realized the gap is too much for that to work. The sill tray would close that gap a bit, but there would still be a place for snow and rain to get into. I'll get all that stuff out of there before putting down some new concrete. Is this the right way to do it? Any help would be much appreciated!