I baked 3 cakes that I plan to stack and ice with buttercream. I used a different brand of cake mix and each of them partially stuck to the pan on the side despite the fact I greased the pans well with butter. A few chunks came off in the process. When I crumb coat it, is it possible for the buttercream to completely fill the gaps and still achieve straight smooth sides? Or should I just start again? Wanting to make the cake as perfect as I can for my son’s 1st birthday