Is what I did by moving the curtain away from the Qur’an, and letting it fall upon it when standing for prayer, considered an insult to the Qur’an and does it lead to disbelief?

What you are experiencing is not an insult to the Qur’an nor does it lead to disbelief; rather, it is satanic whispers (waswas). The most beneficial cure for repelling these whispers is to ignore them and pay no attention to them, to turn towards the remembrance of Allah Almighty and increase in it, and to rejoice in the whispers to infuriate Satan. Whoever listens to these whispers will find them increase until they drive him to madness, whereas whoever ignores them will find them disappear after a short while. Whispers are from Satan, and his goal is to lead the believer astray. Their cure is to believe that they are a satanic thought and to fight them as one would fight an enemy of Allah.