Since it is in essence a return service, I see no problem. There will have been plenty of moves that have done essentially the same thing (gone part way down a branch line, crossed the platform and come back on what turns out to be the same train on its return journey) which would be acceptable on the grounds that they are different services. My understanding of the rule is that you are not permitted to get onto the service you have just left (i.e. stepping onto a platform and getting back on the same train). There's no particular comment on services that happen to call at a stop/station/jetty/whatever twice in their journey. On balance, I would claim that my move was in the spirit of keeping us moving, and since the ferry we got off had already departed and was heading back in the direction we came from, I think it's perfectly reasonable. Ferry services are often presented in this way - where a return service to a destination and back again is listed as a single service, whereas on the railways and buses such services would be listed as separate journeys.
But if you particularly want us to wait for the 14:00 service (that gets us back into Venice San Zaccaria at 14:10, all other details the same) then go ahead.
