Can't help you, I have my own problems since watching "Back to the future" yesterday.
Basically, at the end, Marty goes back early to warn the Doc about getting shot, only to be too late - he sees the doc shot and he also sees himself escaping the Libyans and going back in time. This means that some sort of time loop has been created, and that there is another Marty(#2) in the past who is destined to come back early as Marty#1 did, where he will watch Marty#3 go back in time...and so on adinfinitum (nauseum). In the meantime Marty#1 (etc) gets on with his life.