To get back to the scale you had, you could print off one page which contains a part you already have in your build (you can use regular paper for this, no need to waste cardstock), cut out that part and compare it to the existing part until they match. Once you have it figured out, save the PDO. If you don't have the key to Pep Designer, then print off the 2D pages as a PDF, then you'll have it forever.