Thank you all for your answers, actually I used a dam but I definitely went overboard with the filling it was as thick as half a layer, next time I won't go over 1/4, or over my dam. It was really a looot of mousse in the middle but I definitely learned my lesson. Thanks again!
I made a 2 tiered cake filled with chocolate mousse, as I was finishing decorating it... I saw that some filling was coming out of it. When we got to cutting the cake the top tier just slided of! Could it be that I used to much filling? I just feel so bad about it.