you dont need to put any trim on the edge as its a factory edge not a rusty 1, also you had better get the welder put where you have cut that edge away, as you have removed half the spot welds
If it was factory welds I would agree but I've replaced boot floor, valance and hinge panel ...... Don't worry it's more than capable of not having that 15mm extra lip....:0).... I've seamed welded the whole length of the rear inside....as well as spot welding the lip near the body aswell
Cheers James