If you don't complete the game you just enter your final score.
However if you complete it, you get a bonus of 100.000 points. To avoid leeching you must subtract 10.000 points for each life lost. You lose a life by either dropping into the water, or if the time runs out. Here's the scoring system formula to use if you complete the game:
Final Score + 100.000 - (X * 10.000)
X = Number of lives lost in the game.
There's also a Side Competitions for this game in which you can leech as much as you like.