Nook HD - PDF Conversion Size Issue

[jkusmc]

I am trying to convert some National Geographic from PDF to ePub. When I convert them, they come out either too small or too big, depending on the device I select. The books come out perfect as far as layout, but they are either blown up (with about 1/3 of the pages cut off) or in the smaller conversion the magazines come out taking up only about 1/3 of the screen.

I know people are probably going to tell me to just keep the PDF, but I would like to get these to epub if possible. Any help would be greatly appreciated. Thanks!