How can I stop dots material from stretching over sphere object?

Hello, I've just started using Dimension today and I'm trying to create a 3D model of a Spikeball (picture of desired end result)

The problem I'm having is when I apply a polka dot substance material to my sphere, the dots stretch into ovals. Is there any way I can prevent this from happening so the dots stay circles?

This is what I have so far: spikeball-1