why get back in the car...???

Well it's sort of the premise of the film that history repeats itself. They were destoned to die in that car the same as before.

This is beyond you Metal Man. -Thor
Formally known as Una-Flux

Like it was written on Jimmy's school blackboard: "What's done cannot be undone. -- William Shakespeare" History repeats itself. That's the whole premise of the movie. They died in that car and are destined to die again the same way. You cannot change what's already been.