Rectangle guide creating new layers with every brush stroke?

TiltBrush noob here

Every time I try to use the rectange tool to make a consistent and flat design, every new brushstroke seems to be on a slightly higher layer. This wouldn’t be too bad, except that shrinking down makes the layer imperfection extremely obvious, turning a flat plane into a strange looking block with dark lines everywhere.

Is the rectangle guide slightly expanding with every new brushstroke? Does it push the layer down with every brush? Is it something I can fix in the settings menu?