Knit 1, 2, 3, 4, 5, 6, 7, 8, 9...THEN knit the 10th and 11th stitch, and bind off the 10th stitch over top of the 11th stitch (1 st is now bound off)...and continue the bind-off count. I think you misconstrued the part in blue. AFTER you knit the 9 knits...you need to knit two stitches more (10th & 11th) before the binding off 'count' clock starts ticking.
I think this is where your extra stitch came from. Try it.