When we sailed to St Thomas on Carnival. We paid taxi driver to take us to private beach and he assured us he would be back at a certain time to get us back to ship on time. Well, after waiting 20 minutes and he still was not there, we hailed another driver and barely made it to the ship on time. We had already paid 1st driver, so I would go with the driver and pay him upon picking you up for your return trip to make sure he comes back for you. That is always my greatest fear is missing the ship!
Good luck, and have a gret trip. We have booked a 10-07 Western cruise with C. Princess we are looking forward to.