Don't return it yet. The download took forever because of the mass amount of people downloading yesterday.
As for the book, it's not registered to someone else. I know the process in the UK is different, but what that code amounts to is that you bought a "secure" ePub, and you need to set you Reader up so that it can read them. In the US, after you sign up for a Sony account, after a half hour or so Sony will create a Adobe user ID for you that is the same as your Sony account, and then you are good to go. I believe it is different in the UK, and you can either search the forum or wait for a UK user to chime in. I believe you will need to download Adobe Digital Editions, which is free, and hook your Reader up to that program to authorize it.
Please don't return it yet
But I can say, don't ever synch. That feature has never worked well (I don't speak from experience, I've never tried it).