I am doing a poker chip cake for a friend's party. The cake is three 9 inch double layer round cakes, covered in fondant and decorated to look like a stack of chips. Two are side by side on a large rectangular board, and one will be going in the middle between the lower two (kind of like a triangle. I put dowel rods in tonight and plan to put the top layer on tomorrow, but it occurred to me that because of the fondant decorations on the lower cakes, they are not completely flat so the top cake may not rest evenly across, but sag a bit in the middle. Will this be okay the way I am doing it? It may settle a bit, but I don't know how much yet, since I haven't done it. is there anything else I should do for support?

Can you move the two lower cakes closer together so there's no room for sag? Or put your third cake on another board for sturdiness?