Exporting pdf from libredraw changes trim size on document?

I export a document from librewriter to pdf and the trim size is great. 5.5"x8.5". But I have to edit the pdf due to page number/header issues I can’t fix with writer, so I go to libredraw and make the changes there. I have to export it again to pdf, but when I do it changes the size to 5.48xx by 8.48xx. When this happens, I am unable to upload it to createspace to use as a document. How do I keep Draw from changing the size of my document? I have it set to lossless, I’m not sure what the issue is here. It has to be exact for book printing.