I don't think that you are going wrong. Sizing photo's to print on an inkjet is very complex. Epson provide software on recent photo printers that do this automatically. I have one of these which takes up 53.6 MB of disk space indicating that this is very involved. Consider Adobe Photoshop Album (tryout download available) which is a powerfull storage, enhancement and printing package that will enable you to select print sizes from 2.1" x 2.8" in five increments up to 10" x 8" plus custom. Cost about £40 but well worth it.