self.contents.blt(4, 32*index, bitmap, Rect.new(0, 0, 24, 24), opacity)
Use this instead:
self.contents.blt(164 - j * 28, 32, bitmap, Rect.new(0, 0, 24, 24), opacity)
The the icons will move as well. If it still doesn't work, try putting your two commands below the code you just posted, after the second "end".