Is a person considered an infidel if he imagined the Angel of Death speaking to him and asking him: "Do you want to die today?" and he replied: "I do not want to die tomorrow," knowing that his intention was not to mock?

This statement does not lead to disbelief (kufr). Angels are sometimes seen and spoken to by some people. If you are lying in what you have claimed, then repent to Allah from the forbidden lie, increase in righteous deeds, and prepare for death.