Why is my touched script not detecting a block?

so right now i have a script (below) which is a placement script. there is a part below which is supposed to see if a block is being touched then turn it red but it isnt working too well. (vid below) https://streamable.com/fx84wh

wait()
local Players = game:GetService("Players")
local player = Players.LocalPlayer 
local mouse = player:GetMouse()
local plan = game.ReplicatedStorage.Wall.Selection
local build = game.ReplicatedStorage.Wall.Place
local pos = Vector3.new(0,0,0)
local a = 0
local canplace = true
script.Parent.Equipped:Connect(function(mouse)
	local plan1 = plan:Clone()
	plan1.Parent = game.Workspace
	mouse.TargetFilter = workspace.Selection
	mouse.Button1Down:connect(function()
		if canplace == true then
			local build1 = build:Clone()
			build1.Parent = game.Workspace
			build1.Position = plan1.Position
			mouse.TargetFilter = workspace.Selection
		end
	end)
	local Model = game.Workspace.Selection
	while wait() do
		game.Workspace.Selection.Touched:Connect(function(Touch)
			if Touch:IsA("Part") then
				Model.Color = Color3.fromRGB(255, 0, 0)
				canplace = false
			end
		end)
		game.Workspace.Selection.TouchEnded:Connect(function()
			Model.Color = Color3.fromRGB(0, 255, 0)
			canplace = true
		end)
		pos = Vector3.new(math.floor(mouse.Hit.p.X),math.floor(mouse.Hit.p.Y),math.floor(mouse.Hit.p.Z))
		plan1.Position = pos+Vector3.new(0,6,0)
	end
end)
script.Parent.Unequipped:Connect(function()
	workspace.Selection:Destroy()
end)

heres the part that supposed to detect the touch

game.Workspace.Selection.Touched:Connect(function(Touch)
			if Touch:IsA("Part") then
				Model.Color = Color3.fromRGB(255, 0, 0)
				canplace = false
			end
		end)
		game.Workspace.Selection.TouchEnded:Connect(function()
			Model.Color = Color3.fromRGB(0, 255, 0)
			canplace = true
		end)

please help me fix this

You must use touch:IsA("BasePart") instead of just "Part"