How do you get off shrink ray island?

Answer 1

To leave without completing the island:

You climb up on the computer desk in CJ's bedroom, then onto the computer then you jump onto the wall thermostat, and turn the dial by running on it. Once the red light goes on, head left to the other side of the bedroom and knock over the wastebasket. Use the floating objects as stepping stones to get up onto the bed, then jump over the fan. Once you are on the floor, jump up onto the drawers and then climb up onto the rope and head off the island.

(see the related question)