Thanks GG for the sleuthing.
Yes, so the pattern is counting the stitch left after the bind off as one of the K8 sts in the repeat and as one of the final K5sts. Do the same thing you just did, bind off 10 sts (that leaves you with one stitch on the right needle), but then knit the next 7sts. At the end of the row bind off 10 and knit the next 4 sts and the numbers will work out. You'll have sections of 10 bound off sts with 8sts on the needle between them.
Row 7: K5 (BO10, K7) 5 times, BO 10, K4
Row 8: K5 (CO10, K7) 5 times, CO 10, K4
Very clearly written patterns make a comment about how to count the stitch left after the bind off in the next instruction.
Looks like a fun knit. We'd love to see photos of the finished scarf.