The film. BTTF works if you take into account the notion of multiple universes. For every decision that you make, a universe is created to act out each one. BTTF2 explains this pretty well, and shows that 1955 is some kind of nexus point where all events seem to pivot on.
You shot,d listen to the radio more. They got that bit right.
Marty’s life and perception of it is not changed. He goes from his original life > 1955 > new life. He does not automagically *become* the Marty of the alternative world he lives in. His reaction shows that he’s not lived that life. However, kit’s obvious that for one reason or another, the Marty from that timeline has also vanished. It’s likely that in all universes, Marty has to travel back to the 1955 nexus point.
As a big, big punishment. You can also keep your eyes on them.