Hi,
I can imagine why you'd think your map would be better suited in a map of your own making, but we want everyone to start on the official contest map, so as to keep the judging process fair, and not discriminate against users who don't know about terraforming.
However, we do allow users to modify the map, as long as we can see that you used the official one. Therefore, I think the best solution, if you really want to use your own cavern, is to terraform one near the starting cave, build your project in it, and then use the starting cave to build some sort of entrance, or a build that will lead to the second cavern where your main project is.
With this, everyone will be happy: you because you will have used your own cavern for the main build, us because you will still have used the starting map, and the users because they will have two caverns with pretty things built in it
