How do you know you're cooked?

Hi everyone, I'm pretty new to the game. There are some signals that I can't properly sense for now. Like, when should I understand that the game is lost/there's no coming back? For instance, these days, I'm playing USSR against a friend who is leading the general score at 13pts in the end of turn 5. I'm only ahead in Europe and SA. I read somewhere that USSR are supposed to be ahead on general score during the first part of a game. Should I consider the game as lost? At this point, my only hope is a win in Europe, but it seems that the U.S. are getting stronger in this area as the turns go by, because of their cards.