Placing Block Outline (Unsolved)

Help and Feedback Scripting Support
#1

I need to make a placement showing outline for my single use wood block item

local in it:

local Mouse = game.Players.LocalPlayer:GetMouse()
local Positiona

script.Parent.Activated:Connect(function()
	script.Parent.place:FireServer(Positiona)

end)

Mouse.Move:Connect(function()
	local GridSize = 3
	local X = math.floor((Mouse.Hit.X + GridSize / 2) / GridSize) * GridSize
	local Y = math.ceil((Mouse.Hit.Y + GridSize / 4 ) / GridSize) * GridSize - 1.5
	local Z = math.floor((Mouse.Hit.Z + GridSize / 2) / GridSize) * GridSize
	Positiona = CFrame.new(X, Y, Z)
end)

server script in it

script.Parent.place.OnServerEvent:Connect(function(player, Positiona)
	local shape = Instance.new("Part", workspace)
	shape.Size = Vector3.new(3,3,3)
	shape.Material = script.Parent.Handle.Material
	shape.Anchored = true
	shape.Color = script.Parent.Handle.Color
	shape.CFrame = Positiona
	print("BlockPlaced")
	script.Parent:Destroy()
	shape.PivotOffset = (CFrame.new(Positiona))
	end)

(it has a remote event in it too )

I wanna make it so that it can show a outline of where the block will place ok?

#2 
local Positiona

local a = Instance.new("Part")
a.Size = Vector3.new(1,1,1)
a.Anchored = true
a.Parent = workspace
a.Material = Enum.Material.Plastic
a.Color = Color3.fromRGB(102, 255, 0)
a.CastShadow = false
a.CanCollide = false
a.Transparency = 0.5

Mouse.Move:Connect(function()
	local GridSize = 3
	local X = math.floor((Mouse.Hit.X + GridSize / 2) / GridSize) * GridSize
	local Y = math.ceil((Mouse.Hit.Y + GridSize / 4 ) / GridSize) * GridSize - 1.5
	local Z = math.floor((Mouse.Hit.Z + GridSize / 2) / GridSize) * GridSize
	
	a.CFrame = CFrame.new(X, Y, Z)
end)
#3

The outline isn’t the right size and it also is always visible,
the block doesn’t place either, it also has no errors