Can't revise margins

[Milton]

I am trying to save/print a one page document from Scribus to a Bullzip PDF, but can't seem to get the margins correct. My document is a book cover with bleed edges 11.68 inches wide x 8.25 inches high. I have tried to set the document margins in both Scribus and Bullzip first with PostCript custom page, then by creating a new document size in the printer settings. What happens is that the PDF appears to be the correct width, but the height is off about .25 inch. On other attempts, I get white space margins at the top and bottom. Earlier versions of the document were 8 inches high and I revised it to 8.25 inches to get proper bleed, but I keep getting the shorter result in the PDF. Any suggestions? -- Thanks.