CC Parasailing Booking Question

[caribbeandreaming]

My DH and DS (8) decided they would like to do parasailing on our cruise in a few weeks. I figured it was sold out and got excited when it wasn't grayed out when I logged in to check. As it turns out, it's not sold out but there's only 1 opening as it allowed me to book 1 person but not 2. The 2 of them want to go up together so it's not like adding my DS would cause them to do have to do another launch. I do know that the boat probably has weight limits, but if it's an 8 year old child, it's not going to add that much. Has this happened to anyone else? If so, did DCL allow you to add a child?

Also, when do you have to cancel this excursion in order to not have it charged to your stateroom? We may try to book again after getting on the ship, but I want to know that I'm able to cancel it if that won't be a possibility.

Thanks!