On Windows operating systems, depending on what printer you have installed, you will have a different set of print settings as opposed to your Vectorworks Page Setup settings. These settings are usually detailed in the documentation for the specific printer.
Under File > Page Setup, make sure that Horizontal and Vertical are both at 1 and 1 and that Choose Size Unavailable in Printer Setup is set to One Printer Page. Use Printer Setup to alter your paper size. DO NOT manually change Width and Height in Page Setup or your print will not be scaled properly.
Mac OS X:
A common issue on Macs is that the margins or paper size will not set properly. The Mac OS is easier to troubleshoot as all of the print setup options are the same for every machine, unlike windows where each printer will have its own variation of the printer setup.
Go to File > Page Setup
Users will often assume setting the page size to "Arch D" or "ASME C" will make their printer choose that paper size, this is incorrect. The setting here is telling Vectorworks the Page Size, it is not instructing the printer to use a specific kind of paper. The "Horizontal" and "Vertical" boxes on the top left corner will always read 1 and 1 when configured properly.
Under Printer Setup, select Manage Custom Sizes under Paper Size. At the bottom left of the screen, click the + icon. This will allow you to add a new custom paper size. Create one custom paper size for each type of paper you wish to print on. Set the Page Width and Height to the desired size, then make sure to set all of the Printer Margins to User Defined: 0"