Diana 350 magnum crown - is it normal?

Yep, every review I read was nothing but gold stars. Tack driver, one bug hole at 25yds, etc, etc. That's why I got it. Wanted to own something really accurate and also useful for pest control (accurate enough for a rat's head) or light hunting. Just didn't work out that way (as far as one shot, guaranteed clean kill goes). Reading above it sounds like there were at least two of us with the "bad crown" syndrome. Not what you'd expect at that price point is all I'm saying. This should have been a finished rifle, not one with the disclaimer "some gunsmithing may be required" on it. Just trying to find solutions / suggestions via this forum to fix what's "not quite right" at this point, short of an expensive gunsmith bill.