Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, that choice is available by clicking the chevron to the right of the Save Project button on the toolbar.
Then close the current project. When you want to reload it, double-click the most recent VPJ that you saved.
Prior to beginning a new project, open OPTIONS | DISK tab and Clear Unused Cache Files. You can also do this while working on a project.