When choosing the print options in Gantter, you can choose to generate PDFs for the "Task List" and the "Gantt Chart" separately or together. This helps it fit better on one page when printing.

Gantter generates the PDF as a single-page. The steps to break it up into multiple pages so the print is larger depends on your PDF software and your printer. This link can give you instructions to print as multiple pages using Adobe Reader.

You can also try choosing the "HTML" print option from Gantter instead of PDF. You can then print it the way you would print any web-page.