When you started the band, the pattern states to use provisional cast on. How did you cast on?
When you use the prov. cast on, it allows you unravel part of the cast on row, this gives you live stitches. You'd put your extra needle in these live stitches, and then kitchener (graft) them together.
Assuming you haven't done the prov. cast on, you can seam them together a different way that won't show your seam...mattress stitch might do the trick.
As far as your band, if it fits around your head nicely already, then your gauge might be off. You can keep going as you are, as long as you have enough room around the band to pick up 84 (or more) stitches.
Hope this helps...