PrintOMatic prints RTF ("text") members as bitmapped images, not as styled text. This has to do with the pre-D7 legacy of RTF members, when Director would strip out all the text from these members in Projectors.
The way that PrintOMatic handles bitmaps is to shrink them to fit on the page. As a result, long RTF members will print out at impossibly small sizes on the page.
Click here for detailed information about text members and PrintOMatic.
The best quality printing with PrintOMatic always comes from using text FIELD members. Consider placing your printable text into these members for best results.
Your other option is to split your RTF into multiple one-page members and print them sequentially, e.g.:
print member 1, member 2, member 3
To view this and other technical notes on-line, visit http://www.printomatic.com/tech.cfm.