bamboo flattening

Hello I just need a little hint on how to flatten bamboo properly. I was able to remove a few strips from a 3.5" diameter staff, 27" long and 1.5" wide, node in the middle. I scored the bamboo and soaked it for a week. When I heated the bamboo up and attempted to bend it; it split along the scored areas I made. I have Thomas video but there isnt enough detail for me to figure it out. Any help would do.
How deep should I score and how much should I clean the bamboo before I soak? thanks Victor