Hi Hegartype,
It sounds like the issue is that the canvas is too small to accommodate the cutter around the STL model. You might be able to get away with just disabling the "Confine Cuts" option on your operation parameters, which will effectively open up the canvas by half of the cutter's diameter so that it can cut outside of the canvas. This will only allow the center of the cutter to reach the extents of the canvas volume in X and Y, so if that still doesn't allow for enough room then you will still need to open up the canvas' dimensions a bit further.
Let me know how it goes!
- Charlie