After you have paid your print fee, you'll be fedexed a mock-up of your book to review. You are about to print at least a thousand copies. At this point you are in a delirious eager rush. Calm down. After the printer prints a proof-version, the author or editor (or both) proof-read  the manuscript one more time before printing. Check it carefully. Make any necessary changes.

You might elect to take the cover into a friendly   bookstore and ask them to scan the bar code to make sure it appears on books in print, with  all of the information correct. This will be positive proof that your bar code is correct. You'll note, occasionally, that a book in a store has a bar code applied as a label. In some cases,   this is the result of an error, and the fix is costly and easily avoidable.

And not to worry too much, if there are errors, you can fix any problem in the next run.