My Car Model

I'm trying to modelling a car and thats not as easy as i expected. it's difficult enough when adjusting the vertices to get car shape balance. This not good enough when you look at the car model it have a line in the middle of the car body. That comes when i apply the mirror modifier on the car. Image below is my car body model. Next i am planning to make this model into a FULL car. Ya.. i need more practices..