2018 FIFA World Cup Prediction Contest

So, for example, if I bet on a 2-1 score, the main time ends 1-1, and in extra time it becomes 2-1, do I get 3 points?

That's absolutely correct. And there's no need for any complications or redundancy. The match ended 2:1.

As for penalties, they are called post-match penalties. And we make predictions for matches.