Hi @sevildi,
I've looked at your file and I think I need to clarify for you the difference between at canvas and a decal.
Canvases are images you put place as reference on a 2D plane to use as reference when modeling. They are not seen by the rendering engine as being associated to geometry in the scene. Which is why when you try to render them you see this:

Decals are "stickers" or "labels" that you place on your geometry. The decal system in Fusion 360 is different than other software programs in that it creates a mesh file the size of the image file that you are using as the decal and attached the image on the mesh. This allows you to move the decal around an area of high curvature on a model without seeing stretching. Most other software programs use some type of projection map technique for labels which can show stretching depending on the surface it is being applied to.
The downside to the technique used in Fusion is that the mesh file can create problems around corners like you seeing in your model.

I suggest you create a texture map (or use a premade one from the library) as the base material for your box and then make individual decals for the lettering/logos and assign them to the surfaces individually being careful not to go past the edge of the face. In my example below I replaced the "paper" material image with a tileable cardboard texture image that I found here:http://ftextures.com/texture.php?title=Tileable-cardboard-texture.

To replace the existing image on a material:
- Select the material from the library you want to edit and assign it to the part (library items are locked and cannot be edited)
- Double click on the material swatch in the "In this Design" section of the dialog box
- Click on the Advanced button to open the advanced options
- Under the image you will see the location of the image source for the material. Click on that to select a new image.
- Select the new image from your computer files


Hope that helps,
Colin
Colin Smith
Sr. Product Manager
SketchBook
Alias Create VR (aka Project Sugarhill)
Automotive & Conceptual Design Group