You always, ALWAYS print from Desinger. Viewer has little to no use when it comes to scaling and printing a file.
After you adjust the scale, move the pieces around, and if needed, cut them or moddify the unfold to make each piece is inside of the dotted grey lines. Also make sure the printer paper settings are all correct. If you plan on printing using Leter paper, make sure you have Letter selected. Same goes with A4, and so on.
Also make sure you have it scaled right. Remember, measure twice, cut once. (or, in your case, measure twice, pep once.)
Good luck!