Hmm looking at the rear diff better I think it needs to follow all the way to each side of the car. Kinda like this, excuse the 5s mspaint job, you get the idea.
Also, from profile it just looks like something is hanging off the car's butt, maybe extending the piece towards the front of the car where the wheel arch begins. From yellow arrow to the red line shown here:
While I am at it, here's another suggestion
How about extending the CF piece in the fender all the way down to the side blade. Like this:
Side profile with extended fenders and extended rear diffuser to wheel arch:
Anyway, just my opinion