Let me explain you why this scene is really, like really really important, for Edmund. Since he betrayed his brother and sisters in their first time in Narnia, Edmund tried really hard to redeem himself. Not only by becoming King Edmund the Just (The Lion, the Witch and the Wardrobe), but also by supporting Lucy when she said she saw Aslan (Prince Caspian), helping Peter when he fights Miraz (Prince Caspian), joining Caspian looking for the seven lords (Voyage of the Dawn Treader) and much more. He is, and forever, marked by what he did when he was only a kid. A kid mad at the world for making him go away from his mother, from sending his father to the war. I’m not saying that he has to be forgiven, but understood instead.
As it was said, your worst nightmares came alive in there. So when he sees Jadis, the White Witch, he freaks out. I mean, she embodies the past he tries so hard to forget. He has to face, again, what he regrets so much. He is scared. Jadis manipulated him when he was young and naive. And she is trying it again. So, let’s not say that Edmund betrayed his family and he doesn’t care, or he had moved on. Because that’s not true. You can see it in his face, he still struggles with that. He is far from have moved on.
“All their life in this world and all their adventures in Narnia had only been the cover and the title page: now at last they were beginning Chapter One of the Great Story which no one on earth has read: which goes on for ever: in which every chapter is better than the one before.” ― C.S. Lewis, The Last Battle