The editor really looks to be a pixel off sometimes. I thinks that's normal, you don't need to care about it.
Just a point I would to tell you, generally when working with graphics you should use power of 8:
8x8, 16x16, (24x24), 32x32, 64x64, 128x128, 256x256, etc.
That's used for compatibility. Arbitrary number can become a issue.