If you are using Authorize.net, I suggest you enable it and try to place an order on your personal card for a VERY small amount (create an item for 30 cents). If it goes through (shows transaciton ID) in the backoffice and you can see it when logged into your Payment Gateway, you know it is setup right.
AC provides a 'test' mechanism to see fi it is configured properly, but I suggest you try on a live card before you make the payment option live.