A bit of geometry to get you started, placing squares and lines exactly where you want them.
Use half a ball to draw its outline (with a pencil), placing it 3.5 cm from the left edge and 4 cm from the top edge (make sure the ball's attachment is vertical).
Do the same for the other 3 corners of the canvas.
For the balls in the bottom-left and top-right corners, draw a 9 cm square around the ball (the middle of each side must therefore be 1.5 cm from the edge of the ball).
Draw a vertical line: 13.5 cm from the right edge, 1 cm from this previous line, then 0.5 cm from this previous line, then 2 cm from this previous line.