Whoa, the proportions say more max power than car design. Well good effort, the problem is that bmws are more fine art than anything else. The complexity in design is far beyond your current talents and i mean no offense. They play with the way certain surfaces reflect the light in oder to create contrasts of light and dark.
Study BMW design, will do wonders for your design capabilities.
Technique wise, pencil is never a designers tool. First thing they taught us is to never pick up a pencil or a rubber. Either way regardless of that, try and be more conscious of the surface you are mimicking.
