Assuming you've done your homework and really do want the features the 5N provides, I'd suggest you return the NEX-5, even if you have to pay a restocking fee. (You may not even have to, depending on whom you bought it from.) Otherwise, you'll never be able to fully enjoy taking pictures. You'll always be thinking, "if only I'd bought the 5N".
Up to you, of course.
PS. Don't feel too bad. You're not the only one to order the wrong thing online.
Tom