this mousse set up well refrigerated but once i let it stand at room temperature it melts very quickly. Should I add more chocolate next time to l...

Any mousse is a delicate balancing point between the cohesion and the smoothness of the texture.
You said yours melted...does that mean you served it unmolded?
Many (if not most) mousses, like this one, are made, chilled and served in the same container. The container helps hold the mousse, without the necessity of making it too strong in gelatin (as Emmie suggested) or too strong in the chocolate or other flavorings.
I would make the mousse in the individual serving dishes (if you haven't already) and/or chill them longer than specified in the recipe.
Both these may be sufficient to give it the desired texture.

I believe it's supposed to be served chilled, as it says that "the mousse can be served now" after the final chilling step.
The recipe does call for gelatin, though, so if you didn't add any that may be the source of your problems. If you want it to be stiffer, a bit more gelatin would likely do the trick, though it may change the texture to be more jello-y.