The Text won't change when the textbutton is clicked?

I was making something to change the volume of a song for a surfacegui. Once I pressed a button to change the volume sound/pitch, it stays at one, while the sound/pitch changes. Help?

Heres the volume label script similar to the pitch

local sound = game.Workspace.SongBoard.Song
local pitchtext = game.Workspace.SongBoard.Board.Background.VolumeLevel
pitchtext.Text = sound.Volume

Here's the button that'll add the volume similar to subtracting

local sound = game.Workspace.SongBoard.Song
script.Parent.MouseButton1Click:connect(function()
sound.Volume = sound.Volume +.1
end)

Can someone tell me why the text won't change when clicking the button to add volume?