Its set at 100%. When viewed in the skin creator it looks correct, in musicbee it distorted. I did a clean musicbee 3 install on my other laptop and it's the same problem.
with 3.0 bitmap skins, you can't trust the alignment in the skin creator, it's about 2 pixels out.
you have to check the alignment and stretching in the actual compiled skin.
this was mentioned somewhere in the huge GUI changes for v3.0
thread, when I was working on updating my Faded skin
Steven said it was because he had fixed an error that had existed in the 2.x handling