In the File tab, click on Print.
In the first drop down of the Print dialog, choose "Fit to Scale"
Next, choose your scale. By default, the scale your diagram was drawn with will be selected. You'll notice that the paper size is not something you can change. To preserve that scale you will need to have access to paper that size. If you need to print to a specific paper size, you may need to change your scale. You can do so in the drop down for scale in the upper right of the dialog.
After you click Continue, your diagram will be exported to a PDF.
When you print from your PDF viewing program, make sure that it is scaled to 100% or printing to Actual Size so the scale you chose in SmartDraw is not altered. This setting can be bit harder to find. In most browsers, it's hidden behind "More settings".
If printing from Chrome, you can set the Scale to 100% under the Custom option under Scale.
In Edge, the scale setting is also behind More Settings and will be set by default to "Fit to printable area". Check the 100% box instead.
In Firefox, the setting is also behind "More Settings". Uncheck "Fit to page width" and select Scale: 100.
If printing from Adobe Reader, make sure to select the "Actual Size" option.