Er, that's not really the point. Boruto clarified in the Movie that he already knew how to utilize his elemental natures, and Sasuke confirmed during the Hokage Office scene that Boruto was already a strong ninja.
Boruto was insecure about his own abilities because no matter what he did, he couldn't impress Naruto. Naruto kept belittling Boruto's genius, saying that he needs train harder instead of relying on just his talent, to which Boruto doesn't agree because he can accomplish a lot with very little effort.
Hence why Katasuke gives Boruto the Kote, knowing that Boruto wants to enter the Chunin Exams to impress his dad, and that Boruto himself was feeling conflicted about his own abilities.
TLDR: The narrative of the Movie never stated that Boruto wasn't strong enough, but that Boruto wasn't using his full potential. He was capping himself with the Kote.