Holy smokes, that's a lot of names. Nice work! If you want to follow suit with the featured quiz, consider accepting Reg for Reginald and Richie for Ritchie (I don't know which version is actually correct). Also, I definitely typed Dolores, but didn't get the answer, so maybe check that type in as well?
I saw a BuzzFeed website with 708 Harry Potter characters so I think you have missed some. Abel Treetops, Abraham Potter, Abraxas Malfoy, Albert Jorkins and tons more.
I deliberately capped it at 250, as it’s a nice round number and I thought people wouldn’t do the quiz if I tried to go much higher. There were loads I left out, but I will be honest, I couldn’t get to 708!
there are plenty more just from the books, and even more than that from the wiki. i certainly don't think it's a good idea to have some not from the books and not others, which may be from the books.
also, there are some spelling mistakes.