Pincushion has nothing to do with soft focus. Unless you have a Panamorph with a corrector piece it will always be soft at the edges. If you do have the corrector, you may not have the appropriate one. Correctors are pre-set for certain throw ranges. Panamorph make several different ones. If you have the wrong one your image will be softer than expected.
The beam of the projector should pass through the center of your anamorphic lens. You have to tilt, vertically and horizontally offset, and yaw the lens to achieve this. If your projector image is offset to one side then you may have to rotate the Panamorph lens as well, as you will have some slight geometric distortion on the side furthest away from the projector that can only be adjusted by rotation (and then not perfectly).
If you are using offset with your projector, even though the projector casing is level and at right angles to the screen (or should be), the beam will be angled. This - the beam - is what you have to align your lens to, not the projector casing.
If your soft focus is to one side, you might not have the lens centered horizontally on the beam. Even a couple of millimetres out can be critical with prisms. If the softness is at either top or bottom, the tilt of your lens may not match the beam's angle of tilt. It's an iterative process, getting lens alignment right.
Another thing with prisms is that they slightly displace the image to one side or the other, by up to a couple of inches. You can center your 16x9 image and then find that your scope image is offset to the right or left. There's no cure for this, unfortunately. It's a "prism thing". You just have to decide on the best compromise position.
What Richard said about evening up pincushion is right. If the tilt of your lens is not correct then either the top or bottom edge will have more or less than the opposite edge. The sum of the pincushion a lens will induce is shared between top and bottom edges. If your tilt is wrong it can be all to one edge, top or bottom. The aim is to even it up by tilting the lens appropriately, so that the pincushion sum is shared (and thus at least subjectively minimized).
Endless hours of fun and enjoyment await you. When you get it right, you'll know.