I still think you should paddle it for a while- weeks or months- and see if the problem goes away. When you build your own boat you have the ability to change it. If you bought this boat you wouldn't be so anxious to hack it apart. You'd probably try and make it work. I went from a really tight tracking kayak to a Night Heron. Trust me- you have to have good technique to paddle one in a straight line, and it takes some getting used to. What happens if you don't look at your bow when you paddle? If you look at a point on the horizon and look at that spot and not your bow, do you go to that spot, or does it wander radically all over the body of water? Unless the latter is the case I wouldn't mess with the kayak until winter when you've paddled it long enough to have a decent opinion of what its true characteristics are.

m