Looking to ur not smoothed wire, it seems u got some bumps on the side of the car, near the front fender. I cannot help u getting the right curvature,because i think u should only move ur edges/vertices to get it right. Just one last thing, I think that the tail light shape is a bit off, not a circle: I'll delete some edges to get it overall more low poly, so u should be able to handle it more easily. Just my way of working, maybe someone else can help u better!
CPU 2x Intel Xeon E5620 @2.40 GHz
Memory 12 GB Corsair
HDD WD 320GB WD 2TB
Graphics Card Nvidia Quadro FX1800
Monitor Setup 24" Samsung
OS Win 7 Professional x64