I really want to try and switch around our excursion a little once on board, which I heard is possible if you arrive early, but will it be too late to cancel the ones I have now, I didn't want to take the chance of not being able to book anything, so I have a few second and third choices booked. I read somewhere you MUST cancel an excursion before boarding if you want full credit?? I searched for the answer but couldn't find it. TIA!!!!