As you stated, booking with Travelocity - big mistake.
Unfortunately, now you're stuck. Your only recourse is to talk to your agent since they are the ones who control the reservation. Talking to the cruise line will do no good as they will refer you back to the agent.
I would suggest calling Travelocity and demanding to speak to a supervisor. Keep in mind that the people who answer the phone work in a call center, are not certified travel agents, and do absolutely nothing but sell. When talking to the supervisor, if they can't help you to your satisfaction, then demand to speak to their supervisor.
Hopefully, you'll get someone who can help you since, as they admitted, it was their fault in the first place.
First, they cannot book a non-handicap person into an accessible cabin as they have to submit a form to RCCL showing the reason why the passenger needs that cabin. If they fail to submit the form, RCCL can and will move the passengers out of that cabin. If they submitted the form and lied about why the passenger needs it, then the passenger could end up paying the consequences.
As for the balcony, obviously I don't know the cabin you wanted versus the cabin you got, so I can't comment on the size of the balcony. But almost always, except in unusual situations where the cabin is a unique configuration or in a unique location, the balcony for a handicap accessible cabin is the same size or bigger than the same type of cabin that is non-accessible.
But this is one of the major reasons why it's always best to book with a reputable agent than these large online sites since the booking agents do not know or care about anything except selling.