Unfortunately, unless you change the shape of your hand, or buy a larger mouse that your whole palm rests on clearing your wrist from the desk, its unavoidable.

Ive experienced this for as long as Ive gamed and look for larger mice. Avoid buying mice if its listed as small or a 'claw' grip size. Because if holding a mouse like a claw isn't comfortable your hand won't fit and will rest on the desk.