Your skull scarf looks great! Normally, a pattern like that would be done flat, in intarsia, but since the inside won’t be in a position to get caught on anything, it’ll be ok as long as the stranding is kept loose. You can ‘catch’ it on the back to keep it from stranding for so many stitches, which is usually what’s done for long carries across the back.
If you want me to describe it I will, but it’s hard to understand without a picture. Most books that have fair isle in them will show how to do it.
As for intarsia vs. Fair Isle, most intarsia has to be done flat. Sometimes it is possible in the round, but it requires a tutorial all it’s own, and both colors have to be in the inatarsa ‘block’.