take a shotgun patterning target place it out at 25-35 yards fire one barrel at the center circle the pattern with a marker then fire the second barrel at the target same distance and see if they overlap or are off center. if it looks like a oval or a circle your good to go if it looks like two circles or a figure eight the barrels are out of alignment.
unfortunately fixing it requires a lot of money thats why really good SxS and OU are so expensive. i doubt the manufacturer if the price is less than 3,000$ will fix a shotgun that isnt patterning well. most of the cheap ones will if your lucky replace it or tel ya to pound sand its not defective (a little off doesnt count to them) but ya can sure try the warranty route.
a good gunsmith skilled in double barreled shotguns might be able to fix it but its gonna cost a ton of money.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith