Right. And you can add STUPIDITY to the list. If he hadn't admitted going to the marina that day, the bodies would never have been found. I hope the police hang life-sized full-color glossies of the decomposed bodies of Laci and the baby on the walls of Scott's cell.
Peterson's stupid, all right, but I don't believe any sentient human being is that stupid. For what it's worth, my theory is that he did not originally plan to use that same marina as his alibi. When he was there, he must have feared someone had seen him who could identify him later, so he was forced to use "alibi B," that now-infamous "gone fishin'" tale.