I've worked with a lot of hickory and it is one of the woods that really will take any opportunity to absorb moisture and take a set on you. That's just the way it is, that's why most people on here are saying that the ammount of set you have incurred doesn't sound that bad to them. Hickory is a strong, heavy wood, excellent for bows, but may not act like you'd like it to act.
A little set's not always a bad thing too though, as long as you have good tiller. And the only ways to deal with it is to check your tiller, make sure you're not bending too much, especially coming out of the handle, heat treat the bow, put it in your car or truck with the windows up for a few days and then seal it with whatever you use.
But for the length of bow you're working with, you're doing ok. Personallly, I don't think your design is the best for a 68" hickory. A slight bend-in-the-handle with a simple narrow profile with a slightly rounded belly for me is the best (for least set).
~~Papa Matt