I am sure your dealer wouldnt have a problem switching you for a better model if you are THAT disatisfied with your 320. BUT, unless they have a special policy, you cant return a car that is built to order.
But your salesman is right... Those kind of defect happens to any manufacturer; even to the best.
Other then those events; you didnt enjoy the driving at all? That's what you should focus on. You can be sure that your car will be still brand new and in full working order when it gets back from the dealer.