What does the word concocting mean as it is used in paragraph 1? Commonlit

For english i have to find 4 errors in each diary post

The date of a business letter is included in the greeting. heading. inside address. margin.

What is the problem with the following sentence: cameron, who has an extreme and unreasonable suspicion of other people and their motives, suffers from paranoia which is a psychological disorder characterized by delusions of persecution or grandeur, was absolutely sure that someone was following him even though he was absolutely alone and hadn't seen a car for miles and miles.