Ensure you have made all of the parts needed for the cake, and that the cherry filling and ganache have cooled to room temperature, before you begin assembling the cake.
Firstly, you are going to cut the sheet cake into three pieces. To do this, you will need to cut out two 6 inch circles using your cake ring as a guide. The rest of the cake scraps will be used to make the bottom layer, so don't eat or throw away yet. Please see photo above for a guide on the best way to cut the sheet cake.
Place the cake ring on to a board, baking sheet, or plate. Line with inside the cake ring with acetate, taping the ends of the acetate together where they meet.
Using the cake scraps, assemble the bottom layer of the cake inside the cake ring, making sure that the cake is tightly packed and there are no gaps in the layer. Once happy, spoon two tablespoons of the cherry drizzle over this cake layer, trying to make sure the whole cake layer is moist.
Spoon approximately one third of the chocolate ganache onto the cake layer, and spread evenly. Make sure the ganache gets right to the edges of the cake. Spoon half of the cherry filling on top of the ganache and spread out evenly, again making sure to get right up to the edges. Finally, gently spoon half of the whipped cream on top of the cherry layer, spreading out gently to the edges of the cake, trying to avoid mixing with the cherry layer underneath. Try to get the cream layer as flat as possible.
Take a second strip of acetate and gently tuck this between the cake ring and the top 1/4 inch of the first strip of acetate, so that you have a clear ring of acetate about 5 inches tall. Tape the ends of the circle together where they meet.
Place one of the cake circles on top of the cream layer, pressing down gently but firmly with your hands. Repeat the process as before, by drizzling two tablespoons of cherry drizzle over the cake, and then adding one third of the ganache, the remaining cherry filling, and the remaining whipped cream. Again, make sure to get each layer of filling right up to the edges of the acetate, and try to make the whipped cream layer as flat as possible.
Place the remaining cake circle on top of the final cream layer, and press down as before. Drizzle the cake circle with the one or two tablespoons of cherry drizzle - don't use it all if you don't think it's needed. Spoon the last third of the ganache on top of the cake and spread out as before - you've done this enough times to know what you're doing by now!
Place the cake (still on the board/plate/sheet) in to the freezer for 12 hours. This will help join all the various cake and filling layers together. You can leave the assembled cake in the freezer for up to two weeks if needed. Once ready to serve, remove from the cake from the freezer, and gently remove the cake ring and acetate from it. Place on to a serving board or stand, and pop in the fridge for four hours to defrost thoroughly. Serve straight from the fridge, topping with a pile of fresh cherries if wanted.