You can probably get it done easier by ordering the part from PlanePlastics.com. They'll already be the right size and an approved part. It's not cheap, but then again not tremendously expensive. Random blobs of Cessna plastic trim go in the vicinity of $150.
If you own the aircraft, you can possibly make your own part under the owner produced parts, but you'd need to figure out how to draft one identical to what you have and show that it is substantially the same material wise (while a CAR 3 doesn't need certification of the interior materials, you have to show your 3D print material meets the same requirements that the original material had to meet).
