Whenever I make this type of mousse the consistency is always good. However, I know sometimes things can go wrong! If your mousse doesn't seem to be setting, there is something you can do. Combine a tablespoon of cornstarch with either milk or water and stir it into the mousse if it's still liquid. Warm the mousse mixture up in a pan to activate the cornstarch and it should thicken. Divide it between serving glasses and refrigerate it until set. The flavor shouldn't change, just the consistency.