How do I adjust my model preview to the size and view angle I want before publishing
I have tried editing it in the system first. But what I do in the system isn't what is appearing on my preview when I want to publish
Sorry about this, we don't have much control over how the preview image gets generated. The orientation comes from the actual XYZ axes in the CAD file itself, not from any saved views you have in your CAD system. If you are able to modify the orientation of the cardinal axes in your CAD file, you should be able to change what shows up in the 3D preview.
A better option is uploading a screenshot or rendering of the cad model. That way the library shows a better, desirable image instead of the making use of the 3D viewer.
Look at every example on the main library page. None are using the default CAD viewer to automatically create the library image: https://grabcad.com/library
It is better to publish multiple rendered images explaining your design intent, and keep the model for the users to properly view it when they will open it.