dontcallmedora, I'm working on this scarf too!!!!!
I had also found the pattern in the same place you did, and taught myself to knit fair isle because I LOVED the pattern and Hermione's scarf so much. It really is beautiful, but I'm a perfectionist, so I'm a little aggravated at places it's not just right.
I knitted in the round on a circular needle.
I'm really happy with the way it's all coming out, and I'm over halfway done and worked on it like crazy over the Thanksgiving break and am now taking a break because I see stitches when I close my eyes. BUT, there is one mistake that occurred during the whole thing. I somehow added a stitch after the 2nd pattern repeat or so, and that added a white line through the meeting point of every row, and I thought I'd just have to live with it, so I kept knitting a white ( that one extra) every time around. It drove me crazy but I didn't want to take it all out.
Then what happened was I accidentally added another stitch and figured out that I could knit two together
( yeah, I know, where was my mind?) and so I fixed it completely, too bad I hadn't fixed it earlier because now me and my OCD is driving me up the wall.
Oh well... live and learn.
I also don't have any clue how to end it, as I'm not really sure how I figured out the scarf in the first place, so I suppose I'll get back on here and ask.
I'd love to see your finished scarf so we can compare!!!