I suggest reading Robert Sungenis' excellent Flat earth, Flat wrong: "Catholic apologist Robert Sungenis addresses why a growing number of people believe the earth is flat, including the apparently Christian roots of the recent movement. He overviews Bible passages that discuss the earth's shape, the Roman Catholic Church's position on the earth's shape, and historical and scientific evidence for a globe-shaped earth." https://www.goodreads.com/book/show/46194734-flat-earth-flat-wrong Flat earthism is a ridiculous error. Keep believing it if you want. You'll know the truth one day.
Lonewolf: Heaven is in another realm. We will find out where when we die. Hell, some Saints have said, is in the centre of the Earth. Note that Our Lord said He would be in the heart/centre of the Earth for 3 days. That's only possible on a spherical Earth of which Hell is the central core. A flat earth has no "heart" or centre.