Probably a result of the twisted fuselage. I did think of slitting the fuselage joint and trying to straighten it up but I then thought of all the things that could go wrong. The styrene is up to 4mm thick around the cockpit and wing root so it's possible I wouldn't be able to straighten it anyway.
It's a fairly old kit early 2000s I think, not a patch on the kits Valom is making these days which are almost as good as the big boys.