I would be too! But I bet that yarn is delicious! Closest I've ever been to it is to fondle it until the store clerks started eyeing me up strangely.
If you have a kitchen scale you could weigh what you have left - it should be half the skein's weight.
I think before shelling out for a 2nd skein, which you'd only need a little of, I'd reknit them. Maybe even do them 2 at a time so I'd know I was using exactly half the available yarn for each.
I looked the project up at ravelry - you should join if you're not already a member.
Of the people who used the Buffalo Gold yarn, no one mentioned coming up short.