"we had given him nothing, and it made me sad"
Scout uses this phrase to express her sorrow at the fact that they, being the children, had not been good neighbours to Boo. She states, in the sentence before, that good neighbours support one another through crises with gifts, and, though Boo had given them many things over the course of the past two years, they had not repayed the favour. After they found the presents left in the hollow of the tree, they were suspicious, and even after their suspicions waned, they gave nothing in return. Boo had also saved their lives, and they had done nothing to him but inadvertantly torment him and his family through their games and dares. Scout wishes that there were something they could do to make up for the things they had done as children, now that they knew that Boo never meant them harm.