In the main menu "Score", select the tab "Layout" and "Margins".
A new window, "Edit Layout", opens.
Select the tab "Spacing".
Within the part "Default Setup", you can edit the amount of measures per stave as well as the amount of systems per page.
At the right side of the "Edit layout" window, you'll find a preview of your layout. The gray boxes symbolize the amount of your systems per page. Please make sure that all gray boxes are within the dotted line of the white page. Arrange for the number of systems and the margins accordingly.
Confirm your choice by clicking "Apply".