Minecraft is flat. When you sail to one side you don't appear to be sinking like on earth. Done, solved.
I win again!
If minecraft was a cube you would have 4 sides but I don't see 4 sides I don't even see a 2end side below bedrock. It probably is a round world. The neather is something else, probably a world where the mantle should be.
Also, If you go into creative mode and dig straight down to bedrock, break the bedrock, and then go below that, You'll see there's absolutely no curve to the bedrock at all, ever. If it was round like you claim it to be, you'd expect that when moving in a straight line you'd end up back at the hole you came through eventually.
You even see it when there's chunk loading errors:
Flat. Therefore, having space stations appear to orbit something like that would make complete sense: