Aspires filleting is poor. It will only do right angles. What other vector programs do you have? If you have autocad you can import the dxf click on the fillet tool, enter the radius you need and then on the two sides of the corner.

In aspire you can offset outwards by you cutter radius and then offset the new vector inwards by the same amount making sure to NOT have the option "sharp corners" active. Thi however will make other corners also rounded.