At the moment, you can only print sections of the tree. You can maximise the number of people printed by increasing the number of generations shown using the menus at the bottom, but for reasons of space you cannot view all of a large tree. These tips may help you:
To print the largest number of people, select someone in the middle of the tree with many braches coming off them, then increase the generations all to 15.
To print the largest number of direct ancestors and descendants of a person, select the person and increase the number of Parent and Children generations to 15.
It is often necessary to print the tree in sections. Sorry about this, but you could always stick two or more sections together.
Hope this helps!