For some reason I can't seem to fill a cake and not have it bulging out around the sides. What am I doing wrong?

you need to put a dam around the outer rim of the cake with very, very thick BC or frosting and keep filling below level of dam.

@ Patty...Thanks, I do that every time, but sometimes it still does it. Is it a possibilty that the filling is too thin?

I think I just answered my own question.. The BC I had been using was the same consistancy as what I ice with, thin.

The BC should be thick enough that you can make a rope with it and then put it around to outside and then fill with thinner BC or whatever