I know what you guys mean about it not sounding finished, I have an Idea, don't know how it will pan out but I think I'll give it a try.
Make it part 1 of a 3 part song, part 2 obviously more upbeat then into part 3 as it winds back down, like part 1 in reverse. A bit like some of the old prog rock songs with a common theme across 2 or 3 songs.
The final thing will probably end up over 10mins long, but who said tunes had to be 3 mins? lol
Besides I haven't attempted approaching a song this way before, so it will be a challenge