I am in the process of working on my biggest cake I have made yet... I have never made a 12" square cake before and will be baking a 16" next. I greased and floured the pan really well, but a portion of one of the edges still stuck in the pan and when I took it out of the pan it broke .. Its not an extremely big piece, its not even big enough that I could repair it by "gluing" back together with icing. I am wanting to be certain that I can fix this with icing by filling in the missing edge before I put on my fondant?? Or will that edge start to droop under the fondant even if i ice it smooth? If I need it to be perfectly square, do I need to start over??

Of course, you can still use it. . How many layers is the tier? If it's two layers, put that broken-edge layer on the bottom. If it's more than two, put it in the middle. Level your layers like you normally would, without the broken corner. When you fill the cake, put that corner back in there. Trim it to even it. Then crumb coat the cake icing and continue like you normally would. Don't fill in that corner with just icing, because it will droop. I don't know what icing you use, but I chill my crumb-coated cake till set, then put on the fondant. When you put on the fondant, don't overwork it, because the edges will soften and you'll have droopy corners. Otherwise, you should be fine. Good luck!

I had a square cake corner mishap not too long ago...which is one reason why I don't care for Magic Line pans..the corners are very sharp, but they also can tear very easily. Anyway, I made it the bottom layer and crumbcoated and stuck the corner back in, refrigerated it til it was hardened, then shaped it a bit more like clay and then frosted as usual. I refrigerate between frosting layers so it built up quite nicely and stayed put.

Thank you guys! I just didnt want to have to rebake my whole cake, but I want to make sure that it was going to hold up because this is my first wedding cake and I want it to be perfect!!!
@carmijok, this was a Magic Line pan too!! I have a 16" to bake today so I am nervous I am going to tear that one up too!