Watch a video of a rocket taking off.
Actually no. Nevermind. You're right. The earth is flat. Tell everyone you know. Sell all you have and devote your life to something meaningful, like proving the flatness of the earth. Be sure to bring it up every chance you get, especially when no one is asking, that the earth is flat. Strongly oppose and argue with people who disagree. Do not befriend anyone who believes otherwise. The flatness of the earth is in important issue that greatly affects your, and everyone else's, daily life. When you die it's what God will ask you about.