What novel did I say I was a billionaire in high school?

According to the information you provided, this line may come from the novel "The King is Forced by the World".

The King of the World is a systematic science fiction novel, which tells the story that the protagonist Chen Hao is a migrant worker from the countryside. After offending the local bully, he was chased everywhere. As a result, a mysterious old man took him to a secret ancient sect and obtained the legendary system, which enabled him to master astronomy, geography, martial arts and practice the true classics. After that, the protagonist lived a happy life in the secular world with this skill given by the system.

In this novel, after getting this system, the protagonist Chen Hao began to "pretend" on various occasions. In the scene you described, the protagonist may be forced to leave his hometown because he offended the local bully in high school, and he was appreciated by the mysterious old man during his escape and gained a system. After that, he began to use the ability endowed by the system to show his talent and strength on various occasions and won the respect and admiration of everyone.

However, it should be noted that in the novel, "pretending to be forced" is not the purpose of the protagonist, but a way for him to show his true strength and inner talent by using his own ability and institutional advantages. Therefore, although the plot you mentioned in your question is similar to some plots in The King is Forced by the World, it is not certain that you are referring to this novel. At the same time, in real life, don't imitate the behavior in the novel, because such behavior may not only be unrealistic, but also bring trouble to yourself.