The flag is definitely a step in the right direction
The sail could still use a little work. Before submitting you'll want to:
1) Clean up all the shading in the skull. (It might not be shading, but just artifacts from a bad scan... either way, it works better if the skull itself looks clean, unshaded, and untextured.)
2) Make your entire decal about 30-50% transparent (opacity 50-70%). That way the blacks won't be too pure (look
here for color recommendations) and the decal will look more a part of the sail.
If you can achieve both of these objectives I think you'll have a fine decal ready for the game
