Egg... All over my face

So, I realized yesterday that I’m the worst teacher, and maybe the worst person, in the entire world.
In the second grade class, there’s a girl named of Suely (Sway’-lee) who always has a terrible attitude. While everyone else at the start of class is eager to shake hands as we practice the word of the day, she coldly withdraws and refuses to greet me. While everyone else is doing their best work, she circles whatever answer is convenient and easiest to her without the slightest concern for truth. She’s apathetic and grouchy and hardly participates with the class.
Because of her strange and rude behavior, I responded in like unchristian manner. When she flippantly turned in her workbook, hastily and wrongly worked through, I tossed it back at her and told her to do it correctly. When it seemed like she purposefully chose the wrong answers, I upbraided her time and time again to do her work right. I got frustrated, mad, and was very curt with her: “Why don’t you ever try to do anything right?,” I asked her more than once. “You need to learn to do your best,” I told her angrily several times.
Come to find out, though, Suely doesn’t know how to read.
I wish her teacher would have told me a month and a half earlier-- before I got so upset, that is, and undoubtedly shamed this poor girl so terribly so many times in front of all her classmates. Now, though, I’ve got my big old foot in my mouth and there’s nothing I can do except apologize and be more understanding. Once again I’m humbled, but this time I feel like scum, too. I don’t know everything and I’m so human. Shoot.