Inspecting the printer settings to verify and adjust the paper setup is the needed action in this scenario. Making necessary changes in the printer properties or preferences to match the custom paper size specified in the print job will ensure that the document is printed correctly. This includes either loading the correct paper size into the printer or adjusting the printer's setting to handle the input paper size selected by the user. It is crucial that the printer's configuration matches the intended Routput for the custom paper size to prevent it being scaled down to a standard paper size by default.

Choosing 'Calibrate printer' or 'Update printer drivers' is less likely to directly resolve an Incorrect paper size issue and hence are incorrect. While they can be part of broader troubleshooting efforts for various printer problems, they are unlikely to fix a paper sizing-specific error. 'Calibrate printer' generally fixes issues with print quality or alignment, not paper size recognition. Similarly, updating the printer drivers could potentially introduce compatibility for new paper sizes or fix existing bugs, but in situations where the printer already supports the required size and merely is not correctly handling it, calibration or driver updates are not the immediate go-to solutions.