In his testimony, what does Steve say he was doing at the time of the robbery? How does this match or differ from the information we receive through Steve's journal and flashbacks?

During Steve Harmon's testimony, he claims that he was out taking mental notes of places he was going to film for an upcoming school project while the robbery was taking place. Steve completely denies being involved in the robbery and testifies that he was not even in the convenient store on the day of the robbery.
Despite Steve's testimony, the reader knows that he is lying on the witness stand. Steve had written in his journal that he was in the drugstore just before the robbery. Steve mentions that he did not buy anything and was simply looking around the store. When Steve left the store, he did not signal whether or not the coast was clear inside. There are also pictures from a surveillance camera on the pages of the book, which prove that Steve was in the store.
Fortunately, Lorelle Henry did not see Steve in the store or identify him as he was leaving. It is suggested that Steve agreed to participate in the robbery to act as the lookout but changed his mind while he was in the store, which is why he did not give a signal as he was leaving. Steve Harmon's participation in the robbery is ambiguous and his attorney believes that he is guilty even though he is acquitted.
There is also a flashback to Petrocelli turning over a cup while she is practicing with Steve before he takes the witness stand. Steve initially tells her that he was in the store the day of the robbery, and she responds by turning the cup over to indicate that he gave the wrong answer. Overall, Steve admits in his journal to being in the store and lies on the witness stand about what he was doing on the day of the robbery.

In Monster by Walter Dean Myers, Steve is accused of a crime and forced to stand trial. In his testimony, Steve alleges that, at the time of the robbery, he was searching for potential spots that could be featured in his film. If true, that would undermine the argument that he was serving as a lookout. Steve's reaction to the news about what happened during the robbery is certainly one of fear, if nothing else. But his fear does not conclusively prove his guilt or innocence.
In his journal and flashbacks, Steve intentionally avoids any conversations about Nesbitt's death, but that does not itself establish guilt. We can only conclude that he is afraid. Steve is also described as being afraid when he hears about the incident on the news on TV.
So the journal and flashback information does not contradict Steve's testimony, but it does not support it, either. Based on context clues, we can infer that Steve is just a lost soul who is trying to claim his identity in a confusing world.