So the idea is you want your color channel to have more information, i.e. dilate the pixels over edge boundary. Newer versions of Photoshop and PS Elements actually do this for you automatically. This is the "correct" way to do it, otherwise you end up with white edges bleeding across (which premultiplied alpha fixes to an extent, but that can't be used for solid shaders)
The other option, if you'd prefer, is to make the tile "solid" and simply cut the shape using geometry in the sprite collection editor.