Freeair,

Both things seem to be wrong:

The fin will force the fuse to crab to the right when the engine rpms are low.
For all engines rotating counterclockwise, some forces develop at high rpms and take-off that tend to yaw the fuse to the left.
At high rpms, the efects of the fin and the left thrust will be fighting each other.

Can you contact the manufacturer of the fuse and the designer of the model?