How do you make a back button for a music gui?

Hello, basically im trying to make a song gui for a game, but I want to make a back button and its not working. This is my most recent script, and it goes back, but when the song stop it skips 2 songs ahead in the list. I have an idea why, but I dont know how to fix it. If you can, big thanks to you.

local MarketPlaceService = game:GetService("MarketplaceService")

local Songs = {
	4868000543, 
	5546935111, 
	840096159, 
	12345 
}

local globali = 1
local volume = .5

local SongObject = script.Parent.Song
local menu = script.Parent["Music Menu"]
local SongLabel = menu["Currently Playing"]
local SkipButton = menu["Skip Button Music"]
local MuteButton = menu["Mute Music"]
local VolumeUp = menu["Increase Volume Music"]
local VolumeDown = menu["Lower Volume Music"]
local BackwardsButton = menu["Back Button Music"]

MuteButton.MouseButton1Click:Connect(function()
	if SongObject.Volume > 0 then
		SongObject.Volume = 0
	else
		SongObject.Volume = volume
	end
end)

SkipButton.MouseButton1Click:Connect(function()
	SongObject:Stop()
end)

VolumeUp.MouseButton1Click:Connect(function()
	volume = volume + .1
	SongObject.Volume = volume
	print(volume)
end)

VolumeDown.MouseButton1Click:Connect(function()
	volume = volume - .1
	SongObject.Volume = volume
	print(volume)
end)

BackwardsButton.MouseButton1Click:Connect(function()
	local songid = string.gsub(SongObject.SoundId, "rbxassetid://", "")
	local numsong = tonumber(songid)
	local finding = table.find(Songs, numsong)
	local findform 
	findform = finding - 1
	local sing = Songs[findform]
	SongObject.SoundId = "rbxassetid://" .. sing
	SongObject:Play()
end)

while true do
	for i = 1, #Songs do
		local Song = Songs[i]
		print(i)
		local SongInfo = MarketPlaceService:GetProductInfo(Song)
		SongObject.SoundId = "rbxassetid://" .. Song
		SongObject:Play()
		SongLabel.Visible = true
		SongLabel.Text = SongInfo.Name
		wait(3)
		SongLabel.Visible = false
		repeat wait() until not SongObject.IsPlaying
	end
end

Edit: Had to fix some things that were messed up in my post, the post should be good now.

Solved it! I had to remake the sound system so it would work, but it works. The script is below and open source for anyone who wants it.

local MarketPlaceService = game:GetService("MarketplaceService")

local Songs = {
	4868000543, 
	5546935111, 
	840096159, 
	12345 
}

local position = 0
local volume = .5

local SongObject = script.Parent.Song
local menu = script.Parent["Music Menu"]
local SongLabel = menu["Currently Playing"]
local SkipButton = menu["Skip Button Music"]
local MuteButton = menu["Mute Music"]
local VolumeUp = menu["Increase Volume Music"]
local VolumeDown = menu["Lower Volume Music"]
local BackwardsButton = menu["Back Button Music"]

MuteButton.MouseButton1Click:Connect(function()
	if SongObject.Volume > 0 then
		SongObject.Volume = 0
	else
		SongObject.Volume = volume
	end
end)

SkipButton.MouseButton1Click:Connect(function()
	SongObject:Stop()
end)

VolumeUp.MouseButton1Click:Connect(function()
	volume = volume + .1
	SongObject.Volume = volume
	print(volume)
end)

VolumeDown.MouseButton1Click:Connect(function()
	volume = volume - .1
	SongObject.Volume = volume
	print(volume)
end)

BackwardsButton.MouseButton1Click:Connect(function()
	position = position - 2
	SongObject:Stop()

end)

while true do
	if not SongObject.IsPlaying then
		position = position + 1 
		if position > #Songs then
			position = 1
		elseif position < 1 then
			position = #Songs
		end
		local song = Songs[position]
		local asset = game.MarketplaceService:GetProductInfo(song) -- Gets the sound's info
		SongObject.SoundId = "rbxassetid://".. song
		SongObject:Play()
		SongLabel.Text = asset.Name
			repeat wait() until not SongObject.IsPlaying
	end
end