Simplify the following text for a Grade 9 native English-speaking person.
Original: Mistaking Shasta for the missing Prince Corin of Archenland , Narnia 's ally , Edmund scolds the young boy for running off and making everyone worry .
Simplified: Thinking that Shasta is the missing Prince Corin of Archenland , Narnia 's ally , Edmund scolds the boy for running off and making everybody worried sick of him .