Hey! I checked the “Use Subsurf Modifier” option and it helped but still got some deformation as you can see here:
After meddling with the UV editor for a while I kind of got close to what I needed, but couldn’t get rid of the deformation completely. So I deleted the mesh and did it without subsurf and loopcuts:
-Add Plane and extrude in the Z axis for the thickness. No solidify modifier this time.
-Select the 4 edges at the corners then hit Ctrl+B to bevel. No SubSurf modifier either.
That leaves me with one single top face to put my image texture on
-Unwrap (select all with A, unwrap with U)
-Open the image in the UV editor, then assigned the material with the “image as texture” to the top face. That did the trick.
I was overcomplicating things using the subsurf mod + loopcuts for the corners.
Thanks for the feedback, it really helped.