You made just an big fail...
In the "custom_stories/the_tunnel" folder add a file called custom_story_settings.cfg
after that add this:
<Main
Name = "Your_custom_story_name"
Author = "Your_name"
MapsFolder = "maps/"
StartMap = "yourmap.map"
StartPos = "PlayerStartArea_1"
/>
Make sure you've added a folder called maps and putted in it your map!
Add a map folder in "custom_stories/the_tunnel" and make sure you putted there you map and replace the "maps/yourmap.map" and "yourmap.map" with the real map name...
Edit:
I saw the picture rename the folder "my_maps" to "maps" please...