The joys of parenting a tweenager

I've come to the conclusion that I don't necessarily give my child toys and things like that to keep her happy (although I admit I may do that on occasion), rather I give her these things so that I have LEVERAGE when it comes time to discipline her.
Yesterday I had my ultrasound and we left my 11 year old at home, as she's done a few times in the past, for a couple of hours to avoid the inevitable "I'm bored" and "when can we go?" type of whining. While we were gone her job was to empty the dishwasher, as is her job every day. When we returned and I started making dinner I noticed some curious scrape marks on the handle of the refrigerator. When I went to get the bread from the breadbox, I noticed some of the fruit sitting on top of it had similar slash marks on it. After heavy questioning, much denial, and finally threatening to take away computer games, it came out that my daughter thought it would be fun to take a steak knife and hack away at the refrigerator, banana, and pear. After the thoughts of her cutting off her finger or her toe and gushing blood everywhere had gone from my head I think my head exploded or something because the next thing I knew I was yelling at the top of my lungs about the danger of playing with knives-what would you have done if you hurt yourself-that's MY fruit you slashed up-you are not playing any video games for the forseeable future-what on hearth posessed you to do such a thing-madness and she was sent to her room.
I guess she won't be staying home again by herself for some time.
WheneverI end up yelling at my daughter in that way, I end up blaming myself for 1)not instilling in my child that knives are a tool and not a toy and 2) because it's really MY fault that those things happened because if I had been here they obviously wouldn't have but mostly 3)how I must be the worst mother in the world!
Which starts me thinking..."and I want to have another one??". Somehow I convince myself that it will be different this time because THIS time I won't be a single mom. I'll be able to stay home and be around and available all the time. But will it REALLY be? I am 11 years older than I was when I had my daughter (at the just graduated from high school age of 18) and I should be wiser and more world-weary, right? RIGHT??