If my 4x8 goes 1/8" wider than frame am I screwed later???

Building my first build, generic benroy on 4x8 HF frame. Just bought trailer and starting on floor. Here's the future problem I'm worried about, if my outside layer of plywood on my sandwich wall over Laps to cover my ugly red frame rail won't that make my whole build slightly wider that 4 foot. I know it's only gonna be a half inch wider total but wouldn't that come to bite me later when I put ply wood on the roof and when I skin it with aluminum? This is probably a stupid question but it's confusing me and ruinining my sleep!!!! Don't want to mess up or cost myself money this early. Any help would be great! Thanks Adam in KC