deb:
One you establish a template for the disks you're using, i.e , small hub, large hub, etc. you can adjust the printable area in the first window where it has the Outer diameter slider bar and the inner diameter slider bar. My printer came with a cardboard disk that I could use to print a test print, colors and a circle around the outside edge. You need to setup the page size, for the Epson at least, to A4 paper. Don't know what the HP requires. I'm guessing it's the paper size that's throwing off the picture.
Create a test label with just dots at the inner hub, every 90 degrees and at the outer hub every 90 degrees. Then you can print multiple tries on one disk, rotating it slightly each try, to get the alignment correct.