I bolded what needs fixed.
The novel I am in is called A Separate Peace by John Knowles. My name is Gene, and I am sixteen years old at Devon during World War II. I was a very competitive student in academics, and my ambition was to earn the best grades in school. However, I was deathly afraid of sports because I did not excel in them like I did with my academics. My best friend at that time at school was Phineas, a superior athlete. Phineas and I spent a lovely summer together at Devon. One day, because of my jealousy when we were in the tree, I intentionally jounced the limb, which caused Finny to lose his balance, fall, and break his leg. After Finny was released from the infirmary following his injury, he went home to Boston for a while. I visited him there, and I attempted to confess what I had done, but Finny would not allow it.
You could also add some things that happened at the end of the novel: Brinker Hadley accusing Gene of trying to kill Finny; Finny hears this, and he became upset, so he ran out of the room; Finny fell down the stairs, which caused him to break his leg once again; he dies due to his broken leg.
I hope this helps!!!