So i've done thousands of cakes and this has never happened to me until i tried this new chocolate mousse filling recipe, it was quite runny after i made it but since i always pipe a dome around my filling, i didnt expect it to flow out. So after i placed the second layer of cake, of course half of my filling went out. I placed the cake in the fridge to let the filling firm, but everytime i ice it the filling bulges out! I still need to cover it with fondant. What am i supposed to do, the cake needs to be done by tmw!

Honestly I'd take it apart and redo it. If the filling won't hold up outside of the fridge you are just going to keep having problems with it.

You said the filling was runny...??? Mousse should not be runny. Can you share your recipe? A runny filling is not going to make it. Jellies and puddings, etc. need dams, but none should be "runny".

Well the recipe says to melt chocolate with butter and whisk in egg yolks. Whip egg whites and heavy cream with sugar (each in a separate bowl)
and fold both into the chocolate mixture.

Anyway, it looks like theres no solution so i think im going to re-do it

Did you allow the chocolate mixture to cool down before you folded in the cream and egg whites?