It looks to me like most of the handle lines up with the blade just fine, it's just the bell that's a little twisted. Since the bell is generally only going to be used with a hand-and-a-half grip, or if the knife starts to slip, I'd say it's not an issue. If it really bothers you though, all you really need to do is get a file, some sandpaper and some wood finish. File and sand the handle until the outside parts are straight, and ignore the tang. I just checked a few of mine, and they all have asymmetrical tangs, with the scales modified to fit them and create a straight handle. One has a very slightly twisty bell/buttcap, but that one actually has the tang slightly twisted in one direction, and the bell/buttcap twisted in the opposite direction! But the rest of the handle is straight.
It's really just part of owning a truly hand-forged knife. Making perfectly straight, perfectly parallel surfaces is very difficult, and most of their attention goes to making the blade and edge as straight as possible. And like I said, it's very easy to "fix" for yourself, with some basic tools. The balance may still be a tiny bit to one side, but very very few khukuris will balance perfectly.