Hello there ^^. First of all welcome to the forums, yay ; >.
I just played your CS, it is your first attempt so I'm not gonna be a bitch and point out every default. I think you should take a look at the tutorials on this page :
http://wiki.frictionalgames.com/hpl2/tutorials/start
They will help you make basic functions, to use keys, make events...
You are beginning to learn with the Level Editor and you have a lot of things to work on, so I'll just give you one good tip : light up your levels ; ).
Add a boxlight using the Lights tab (the hotkey is 2), and change its size and color so it lights up all your level.
Not much more I can tell you, if you want to make better Custom Stories, just read the tutorials and improve with the editor ! : ).
Good luck, I'm here if you have any sort of questions.