I wonder if you put it down and when you picked it up you went the wrong way. With a k, p pattern, it could happen pretty easily. Did the sts seem funny as you worked into them (I'm trying to think, would the orientation be reversed when you turned but I think not.) I didn't actually do it because I ended up frogging but on one project I decided to go back later and cut the yarn where I had waaaaaaaaaaaaay too much excess and work the ends in. I don't think you'll need to do that.
ETA: Tinking is easier with a smaller needle. I use the smallest I can easily lay my hand on, even as small as a U.S. size 2 when I'm working with any size, even a U.S. 10 or larger.
I should never overestimate my basic arithmetic skills.