Oh dude... seriously?
You ripped it directly out of Metroid Prime 2: Echoes.
And this isn't technically Dark Samus' Theme.
This is "ESCAPE!". It played in the orginal Metroid AND Zero Mission when you needed to get out of Mother Brain's base ASAP. It was revived again for MP2 because you had minutes to escape Dark Aether after killing the Emperor Ing and reclaiming the power from the Sky Sanctuary Temple. The fact that it continued to play when Dark Samus confronted you was to show that you still had a limited amount of time and it was running out, boss battle or not.
Next time, make an original remix or arrangement, and not rip directly from the game.
That's just not cool, man