If you are having resizing issues, that usually originates in the outside design software, when people try to use files that they bought or got from the internet that are (for example) created in one program like Illustrator, in software like Inkscape. It has to do with the default import and export DPI values that get used when saving SVG files. (And every program is different…there is no standard.)
Are you working with SVG files? Some folks have found that using PDF instead helps, and you should always use a 20" x 12" artboard in your design program. It’s the workaround for some of the resizing issues that people run into.
If you want to work with SVG files, there are correct settings for saving the SVG that you need to follow to keep from accidental resizing. Tutorial below for all the majors: