Fitting some body parts together, need advise

[buildinga55]

I am putting the 48 together to make sure everything lines up before I paint and I am having trouble with getting the running board splash apron that goes between the rear fender and body to fit right. This is the part that mounts on top of the running board. I had thoughts of moving the fender back or moving the whole bed back just a bit but I am at about 3/4-1" on the bed space between the cab. Then I thought maybe I should mount the running board first and the panel then try to put on the fender. Seems like there should be a small gap at the front of the panel, but mine at the bottom of the panel is touching the cab. Any ideas?

[LaChevy]

I trimmed the fender end of the panel.

Jim