If the total cost was $7,184, then the company could have retained the entire deposit based on the contract language, and not permitted you to use it toward a different date. That appears to be a concession on their part and they could place restrictions on it since it is beyond what the contract required them to do.
Unless there was a provision in the contract permitting you to cancel within 72 hours without penalty, the contract would normally be binding from the moment you signed it and there would be no right to rescind it for any reason other than a breach by the company. Some people purchase travel insurance
to compensate them for these types of circumstances, but if you did not have travel insurance for which you could file a claim, you would normally be out the amount of the deposit unfortunately.
There does not appear to be anything unlawful about the company informing you that the deposit will be forfeited if it is not used on the scheduled sail date. I'm sorry.
I hope this helps clarify the situation for you. Please remember to rate my service once you have all the information you need so I will be compensated for my time from the deposit you posted with this website. If you have any other questions, please ask me – I’ll be happy to respond. Thank you!