Some scriptures are not meant to be understood as literal. For example the Israelites wandered in the wilderness for forty years. However Hebrews 3:8-9 reads, "do not harden your hearts as in the rebellion, on the day of testing in the wilderness, where your fathers put me to the test and saw my works for forty years." Just as when we might say "in Lincoln's day", we are really referring to the time period when Abraham Lincoln lived, so the day of testing was a period of testing for forty years. Additionally, Jesus spoke in parables. Parables are symbolic stories which teach a lesson. See Matthew 13:36-43, where Jesus gives an interpretation of the parable of the wheat and tares. That story was not about literal wheat and literal tares. 

The Bible nowhere says the the earth is flat – quite to the contrary, the Bible speaks of the earth as round ("the circle of the earth") with the Lord figuratively sitting above it. (Isaiah 40:22)

“Do you not know? Do you not hear? Has it not been told you from the beginning? Have you not understood from the foundations of the earth? It is he who sits above the circle of the earth,and its inhabitants are like grasshoppers; who stretches out the heavens like a curtain,and spreads them like a tent to dwell in” Isaiah 40:21,22

Since the times of the Greeks, educated people knew the round earth's diameter based on measurements done by Eratosthenes (275-195 BC.) They accurately determined the earth’s diameter to be very close to 25,000 miles. This information was understood and believed throughout the Christian world during the centuries that followed.