why does Scout become not afraid of Boo by the end?

Boo saved Scout and Jem from Bob Ewell's attack. That completely ended the childish ideas she had of Boo as a monster. I think she was becoming more aware throughout the book that Boo wasn't the scary man he was made out to be. From the gifts in the tree hole to the blanket on her shoulders, I think Scout knew there was something more to Boo than she had first thought.

I agree with you Aslan. Boo did save scout and jem from bob ewell's attack. and yes that completely ended the childish things scout had of boo as the monster.