I based the shape off of https://www.thingiverse.com/thing:2269715.
The fact that their's has the forward angle forces the center of gravity towards the desk and thus keeps the hook on the table.

The issue I fixed with it is adding the rounded surface that the bag handle hangs from and also removed the angle that the lower "tail" had.

Personally, I add a thin layer of EVA craft foam, super glued onto the bottom of the portion that makes contact with the table, so as to prevent slippage and scratching.

I printed this with 3 layers at 1.5mm with 30% infill and it held up a 10lb backpack and barely had any popping sounds. Lay it on it's side in print setup and it won't require any supports. At least it didn't for me.

Print instructions

Category: Office Print Settings

Printer Brand: Wanhao

Printer: Wanhao Duplicator i3 Plus

Rafts: Yes

Supports: No

Resolution: 1.5

Infill: 30

Filament: Makerbot PLA Black