[Edit] Change collage canvas size in Pic Collage (1:1, 2:3, full screen)
In Freestyle:
1. Click the "Layout" icon on the feature bar.
2. Click on "Size" to change the size of canvas (1:1, 2:3, Full Screen for wallpaper and Instagram Story)
Please refer to the tutorial collages below.
(iOS):

(Android):
