Answer:
Atticus was scared he would miss and shoot the Radley house.
Step-by-step explanation:
Before Atticus actually shoots the rabid dog, Sherriff Tate and Atticus are fighting about who will shoot the dog. Part of the book says that the Radley house was right behind the dog, and that if you missed you would surely hit the house, potentially hurting someone inside. I hope this helps!