Help with SliceCenter on ImageButton

Now for a little bit I’ve been trying to figure out how to use the SliceCenter on Roblox to slice an image into the shape of a button.

What am I trying to achieve?

I’m trying to slice a 50x50 button image with rounded corners into the shape of a 535x40 rectangular button.

What is the issue?

I can’t quite figure out how a 9-slice works. I tried looking at a tutorial but that didn’t work out well, and just left me stranded.
image
Button image. 50x50.

image
Imported into studio and set the SliceScale to 0.25 with a size of 535x40.

What have I tried?

Well, I tried basic solutions that could work for similar stuff like this, but no luck. Help is appreciated!