Enlarging the Canvas
When first started, the Canvas (red box) appears at a default size:
Canvas Controls
The Canvas Controls (located at the top right of the Canvas) appears as follows:
You can click the "+" sign or slide the slider to the right to enlarge the Canvas (up to 400%):
Or reduce it by clicking on the "-" sign or slide the slider to the left to shrink the Canvas (up to 25%):