I'm sorry, I'm gonna be harsh, but I hope you will take my post for what it is intended to be : constructive criticism.
Judging from the ZModeler shot taken from the side, there is a major problem at the back of the car : the rear wheel axle is at least 200mm too much far back, it should be aligned exactly with the frontmost part of the rear wing (the
official 2013 Formula 1 Technical Regulations stipulate this). Once you've done that, you should also move the diffuser a little forward, because it can't extend further back than 350mm from the rear axle.
After that, I can assure you the car will look more natural
Once you understand them, the regulations (mostly article 3 about bodywork) really help shapers make a near-perfection proportioned car. There's really a lot to learn from them.
My workthread
here