Harry has learned that speaking in Parseltongue makes some people hate him and others fear him. He had not learned that it would make Draco go straight to his parents and tell them that he has reason to suspect "Harry Potter" is actually his missing twin brother.
So far, so good 👍 I like it. The fact that Harry is actually the twin brother of Draco, who was kidnapped, is brilliant, a nice twist in the plot.