You are missing an intro, unless you call 2.22 an intro...
You are missing anything to do with a back and forth peaceful idea instead of just white noise
And the darkness can be brought forth through musical emotion... Not just a mono-tone tone all the way through
If you want a good example of an ambient, dark song search up (cave music Diablo 2)
There are a great variety of lessons you can take from such a song, because dark does not usually mean monotone, but rather a deeper, darker feel to the song, which can be made with a contrast of a really deep bass and a deep guitar, then a few high sounds for the contrast
Try again and listen to a few of the Diablo sound tracks before you make your next ambient song