Ruined? That's a great photo! (If you were going for a sort of Halloween effect.) The position of the key light – off to the side and elevated – was perfect for this subject, and is typical of how beauty dishes are used.

Now, if you didn't want the shadow here are things to consider:

1. Using a single source you can't have the subject against a reflective background. So you can avoid shadows by changing the relationship between the subject, light, and backdrop:
   1. Have no backdrop in the frame. E.g., shoot upwards with lightsource pointing down, or shoot against sky. (With a B1 positioned close enough you can choose to drown out the background – even a bright blue sky.)
   2. With a diffuse source as you move the backdrop further away the penumbra will drown out the umbra.
   3. Moving the backdrop back can also make it easier to move the shadow out of frame by adjusting the angle (especially the height) of the light.
   4. Not a good option given this particular subject, but using a very dark background can conceal the shadow enough that whatever is left can be removed with a few simple curve adjustments.
2. Unless you are going for a shadow effect then, when shooting indoors or in close quarters, you need a "fill" light.
   1. Usually this is a second lower-power flash positioned to provide light on the other side of the subject from the "key" light.
   2. Sometimes a "background" light is aimed directly at the backdrop to both blow out shadows and provide a little bounced back-lighting.
   3. You can reduce shadows just using a reflector to bounce from your key light around the subject.
3. Yes, you can remove the shadow in Photoshop, but that's generally more work (especially in a harsh case like this), and not a good photographer's solution to incorrect lighting!