So if the voice is telling you it's wrong, what concerns you about it?
I mean, if you were having problems with the low E falling off the fret, and you adapted so you could confidently play it and get round this problem, then there really isn't a problem in playing it. But yeah, it's not the ideal.
Are you just thinking about selling it and going for something else?
You'd have the same problem even if the neck were bound, you highlighted that the problem was the metric vs. imperial differences, and a bound neck would be exactly the same width as the unbound one.
Did you sink alot of money into this jag? You don't have to give details or anything, but if it bothers you that much that the neck doesn't fit perfectly and you want to go for an all out "perfect" version, then you might just have to bite the bullet and take it as a mistake.
I wouldn't stress about it though, you're a young guy, and you'll probably go through a bunch of guitars in your career.
Aslong as the U.S neck is in good shape, it wouldn't cost the world to get either a U.S jag body or even get a custom body fitted around the neck, by the time you'd ebayed the old body, it wouldn't be that expensive.
