I have been finished (i think so). I cross the mile 3000 without defeating the boss and I started from the beginning. I was thinking than the real final will show up when i defeat the boss crossing the mile 3000.
By the way, this game is awesome, controls are very intuitive but after a while starts to get boring because there is no a second road, certainly the best combination is: 5-3, 3-2, 4-1.