I caught my brother masturbating, was my reaction wrong?

Ok So at the time my brother was around 14, and I was 17. One day I caught him watching and masturbating to, (of all the things) Naruto Hentai on our computer. Bwhahahahaha.
I'm done laughing now. So I asked him, "hey, what are you doing" and he just freaked out and shut down the whole computer.

We're raised in a religious conservative household, and being the older sister who has been there and done that, I really didn't give a ****. But... instead of just walking away, I went downstairs told him either we can make a deal, or I'll tell mom. He would always tell on me and get me in trouble for stupid things, so I blackmailed him with this. Every time he pissed me off I would bring that up. "let me watch tv or i'll tell mom." One day I really wanted him to do something for me, so I swore that I would never blackmail him again with that, and that's how that ended.

Sometime later now that I reflect back upon that... I feel guilty for blackmailing him. I think that was a really nasty tool to use. The same thing happened to me with my sister, she caught me watching girls gone wild once before, (lol I swear it just came on) but she never blackmailed me with it. I feel like a horrible sister to my brother now, and I do things to make up for it. I don't even think he realizes or cares about what happened, but it's really starting to eat up at my conscience. Has anything like this happened to you before? if so, how did you handle it, or get over it. Thanks.