Hey nosediver,
I watched your video and it would be beneficial to see more. From what you've shown us it's too difficult to determine whether you are at CASI 3 standard for everything they will be testing you on. I don't have CASI 3 myself, but I was training for it all last season so I pretty much know what they are looking for. Will is an excellent snowboarder and has his CASI level 3, so definitely take note of his points. From the limited footage I saw these are my observations...
They will definitely look to challenge your riding on steeper and bumpier terrain. As the terrain gets harder, technique flaws become more evident. It would be good to see more riding footage on steeper and bumpier terrain.
Work on shorter radius turns. There is a lot of this in Level 3, especially on the bumps.
Challenge yourself on steeper and bumpier terrain. Make observations when you lose control. Ask yourself why, and try to determine what you need to do to stop it from happening. This will not only help your riding but also help your teaching. Anticipation is a key idea to work on.
Loosen up in your lower body. With down unweighted turns, concentrate on keeping your upper body as still as possible. Anticipate with your upper body, but steer and drive with your lower body.
When carving - sliding in the turns must be eliminated. Work on edging - excellent edging article
HERE from a CASI Level 3 Instructor (training for level 4).
I didn't see any park riding in your video, but that is part of CASI 3 material also. They will test your park riding to some extent. I can't remember the exact details of this but it should be in the course material below.
Check out the following resources...
CASI Level 3 - (from CASI website)
CASI Level 3 course material - (download PDF)
CASI Level 3 standards video: http://www.youtube.com/watch?v=oO2d0vITKnk
STEERING ARTICLE
EDGING ARTICLE
PRESSURE CONTROL ARTICLE
If you have any questions or want to discuss this further, please feel free to do so.