Surely if the Earth is flat, you should have a perfectly to scale 2D world map for it? Because our maps of a 3D spherical Earth needs many different representations of the 3D sphere shape, called projections. Do you have an accurate 2D map?
I hear that if the Earth were the size of an apple, the troposphere (lower atmosphere, reaching far above mountains) would be thinner than the appleskin. So not much difference to a sphere.
I dunno
Could be wrong