Adam's Earth was small, but that does not mean the Earth was small.What is shows is that Adam's small Earth, which had only 4 Rivers which all came from the same source in the Garden of Eden and water his whole world. Genesis 2:10 Adam's small world,inside the bottom of the firmament are at the bottom of a 75 mile wide Lake in the mountains of Ararat exactly as God told us in Genesis 8:4.
What is interesting is that the Ark was above the mountains on the 150th day/5 months AFTER the flood began. Genesis 7:20-24 and ALSO resting upon the mountains of Ararat on the SAME 150th day/5 months AFTER the flood began. Genesis 8:4 If it's so simple, then please explain. Amen?
If there is any consistency to God then the Earth was vastly greater than Adam could grasp and is itself a testimony to God (just as the vastness of the universe, and the depth of the oceans, are for us greater than we know).
It is always an error, IMHO, to read Scripture as if it were a science book.