There seem to be several comments about size and gauge over on Ravelry.
http://www.ravelry.com/patterns/library/finna
The yarn is listed at 21sts/4" and the pattern sems to be calling for 26sts/4" so it's not surprising that you may also be having trouble with gauge. The Fair Isle pattern is going to pull the sweater in a bit but not enough to make up the difference you're seeing There's also a note about a mistake in the chart that you'll want to look at.