I hope that you got off on your adventure as planned and pick this message up somewhere along the way.
As best as I can determine, your sea urchin is Astropyga radiata. It is sometimes called a red urchin and sometimes called a false fire urchin. This urchin is variable in color, but always shows the 5 bands of color that are free of spines. Apparently younger individuals have banded spines. The blue spots are also distinctive. Its distribution appears to be the entire eastern Pacific. In some areas the urchins may form dense clumps of several hundred individuals. This urchin also seems to form a number of associations with other species, some cardinalfishes, some juvenile razorfishes, and juvenile snappers like to hide among the spines, and crabs and shrimp are often found nearby. There is even one crab that may carry this urchin on its back for protection! They seem to be able to enjoy a variety of habitats, from sandy areas to mangroves, to rubble and are found from very shallow to moderately deep water (100 ft?)
Wow, it looks like you might need to go back and check this urchin out to see whether it has friends!
Good luck on your adventure!