When I was five, my brother to babysit me. He and I into a huge fight, and I pretended to run away. I the front door and ran outside. Then I sneaked around and went back inside through a back door. I in my closet for over an hour while my brother searched the whole neighborhood, worried that my mother would come home and find me gone. I it was a great joke. Looking back on it now, I horrible for how much I must have scared him with my trick. I didn't realize how he must have felt.
“Looking back on it now” describes how the speaker feels in the present, so the sentence should read, “I feel horrible.” “Felt” would describe a feeling in the past, but the speaker is explaining their current reaction to the memory.
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