I think you unlock Score Attack mode by beating the game, letting you go back to beat your scores.
I was looking forward to this game, but there are some flaws in it, of course. The fact that you have to buy continues or your saved game is erased automatically is a bit dated. Some of the controls are also iffy, you gain momentum randomly even if it's up hill and suddenly slow down even if you are going down hill.
I like the art style, though, and there is a like of original platformers out there not starring Nintendo characters or licensed shovelware, so I'll probably keep it.