I got to the end of the game where it mentions press something at the title screen to access the secret level. I didn't write it down or take a picture before it disappeared. What buttons do you press? I think it said to press 2 buttons.
Origedit said that the game shouldn't be just horizontal. Skateboards move horizontally, so I think it's fine. I guess in a video game you can create whatever you want, so you could go vertically up a tube or whatever your imagine comes up with. One can tell the game started out as an autorunner, pretty cool work.