I take it that you've ridden in a car, train, and airplane correct?
Each of those systems are comprised of thousands of parts that are based on various engineering principles that in turn are based on various principles of physics which in turn are based on various mathematical principles.
Our entire system of technology is best thought of as a combination of a chain linked fence and a house of cards. There is an interdependency from one principle to another to yet another and on and on and on...
If even a fraction of what you think were true, our entire basis of technology would be impossible. You do not understand the implications of what it is you are saying.
If the world were not a curve, if the world were in fact flat, then that would mean that the force of gravity does not follow the 1/r^2 law. This alone would completely decimate most of our engineering principles meaning that all that technology you take for granted would not work.
if what you say about atmospheric absorption were true, then fiber optics as we know it would not work nor would radio waves or television signals...
in any event, there is nothing I can say that will change your mind. In the next 20 - 30 years, space travel to low earth orbit will be affordable. Perhaps when you go up in space and see for yourself that will change your mind. In the next 40 - 50 years trips to the moon will be affordable as well. Perhaps when you are actually sitting on the moon looking down at Earth you will finally come to believe that the Earth is not flat.