The bible is true because it has proven to be true through the tests of prophecy, preserved manuscripts, archeological evidence, the life and death and resurrection of Jesus Christ, who also said the bible was the Word of God. If a Spirit told me the bible wasn't true, that spirit is obviously a liar and it is not the Holy Spirit. God's spirit NEVER disagrees with the Word of God. N-E-V-E-R.
I will say again: Any claim or teaching that does not jive with the bible IS A LIE.
In all fairness, I fully believe neither the Biblical authors nor those who follow its words ever literally meant it to mean the Earth was flat. But this brings up two points: first, that it is a mistake to expect every single word of the Bible to be completely literal. Second, the case that someone could perpetrate a misconception about the literal word in the Bible is the very reason why the Christian solution is to pray about the passage in question.
As a final note, please accept my apology if ever I gave the impression that I suggested praying to find out if the Bible itself was true. My only intent here was to suggest using prayer when the case of confusion regarding some specific passage may arise.