I don't have a C2 but I'm guessing all of Surefire's clips are designed the same, regardless of size.
If that is the case, then, yes, having the bumps facing away from the light is correct. But are you sure you have the widget sitting in the proper position? The little arms of the T should be resting on top of the metal of the clip.
I've taken my L4 clip off and reattached it a few times for cleaning purposes and it always goes on easy. (By easy, I mean I position the pieces and use edge of table to push all the way in.)