What is wrong with this script?

So I am attempting to create a climb script, its not working.. How would I fix this?

Player = script.Parent.Parent
Player.CharacterAdded:wait(1)
Char = Player.Character
Left, Right = Char:WaitForChild("Left Arm"), Char:WaitForChild("Right Arm")

--Put in starterpack

--Controlls: Q And E

Distance = 10 --How far they can reach

Can = true

Mouse = Player:GetMouse()

Mouse.KeyDown:connect(function(Key)
	if string.lower(Key) == "q" then
		local Q = Left:FindFirstChild("Q")
		if Q then
			Q:remove()
		end
		local Pos = Mouse.Hit.p
		if (Pos - Left.Position).magnitude < Distance then
		if Can then
		Can = false
		local Body = Instance.new("BodyPosition", Left)
		Body.Name = "Q"
		Body.maxForce = Vector3.new(20000, 20000, 20000)
		Body.position = Pos
		local Part = Instance.new("Part", Char)
	    Part.Transparency = 1
	    Part.FormFactor = "Custom"
	    Part.Size = Vector3.new(1, 1, 1)
	    local Box = Instance.new("SelectionBox", Part)
	    Box.Adornee = Part
	    Part.CFrame = CFrame.new(Pos)
	    Part.Name = "Q"
	    wait(0.25)
	    Can = true
	    end
		end
	end
	if string.lower(Key) == "e" then
		local Pos = Mouse.Hit.p
		local E = Right:FindFirstChild("E")
		if E then
			E:remove()
		end
		if (Mouse.Hit.p - Right.Position).magnitude < Distance then
		if Can then
		Can = false
		local Body = Instance.new("BodyPosition", Right)
		Body.Name = "E"
		Body.maxForce = Vector3.new(20000, 20000, 20000)
		Body.position = Pos
		local Part = Instance.new("Part", Char)
	    Part.Transparency = 1
	    Part.FormFactor = "Custom"
	    Part.Size = Vector3.new(1, 1, 1)
	    local Box = Instance.new("SelectionBox", Part)
	    Box.Adornee = Part
	    Part.CFrame = CFrame.new(Pos)
	    Part.Name = "E"
	    wait(0.25)
	    Can = true
	    end
		end
	end
end)

Mouse.KeyUp:connect(function(Key)
	if string.lower(Key) == "q" then
		local Q = Left:FindFirstChild("Q")
		local Q2 = Char:FindFirstChild("Q")
		if Q then
			Q:remove()
		end
		if Q2 then
			Q2:remove()
		end
	end
	if string.lower(Key) == "e" then
		local E = Right:FindFirstChild("E")
		local E2 = Char:FindFirstChild("E")
		if E then
			E:remove()
		end
		if E2 then
			E2:remove()
		end
	end
end)

It's most likely this part:

local Q = Left:FindFirstChild("Q")
        if Q then
            Q:remove()
        end

and this part:

 local E = Right:FindFirstChild("E")
        if E then
            E:remove()
        end

The problem with this is that if "Q" and "E" are nil(Which happens to be whenever the script runs the first time) then the script would break. So I'd propose this as solution:

Player = script.Parent.Parent
Player.CharacterAdded:wait(1)
Char = Player.Character
Left, Right = Char:WaitForChild("Left Arm"), Char:WaitForChild("Right Arm")

--Put in starterpack

--Controlls: Q And E

Distance = 10 --How far they can reach

Can = true

Mouse = Player:GetMouse()

Mouse.KeyDown:connect(function(Key)
    if string.lower(Key) == "q" then
        if Left:FindFirstChild("Q") then
            Left:FindFirstChild("Q"):remove()
        end
	local Q = Left:FindFirstChild("Q")
        local Pos = Mouse.Hit.p
        if (Pos - Left.Position).magnitude < Distance then
        if Can then
        Can = false
        local Body = Instance.new("BodyPosition", Left)
        Body.Name = "Q"
        Body.maxForce = Vector3.new(20000, 20000, 20000)
        Body.position = Pos
        local Part = Instance.new("Part", Char)
        Part.Transparency = 1
        Part.FormFactor = "Custom"
        Part.Size = Vector3.new(1, 1, 1)
        local Box = Instance.new("SelectionBox", Part)
        Box.Adornee = Part
        Part.CFrame = CFrame.new(Pos)
        Part.Name = "Q"
        wait(0.25)
        Can = true
        end
        end
    end
    if string.lower(Key) == "e" then
        local Pos = Mouse.Hit.p
        if Right:FindFirstChild("E") then
           Right:FindFirstChild("E"):remove()
        end
	local E = Right:FindFirstChild("E")
        if (Mouse.Hit.p - Right.Position).magnitude < Distance then
        if Can then
        Can = false
        local Body = Instance.new("BodyPosition", Right)
        Body.Name = "E"
        Body.maxForce = Vector3.new(20000, 20000, 20000)
        Body.position = Pos
        local Part = Instance.new("Part", Char)
        Part.Transparency = 1
        Part.FormFactor = "Custom"
        Part.Size = Vector3.new(1, 1, 1)
        local Box = Instance.new("SelectionBox", Part)
        Box.Adornee = Part
        Part.CFrame = CFrame.new(Pos)
        Part.Name = "E"
        wait(0.25)
        Can = true
        end
        end
    end
end)

Mouse.KeyUp:connect(function(Key)
    if string.lower(Key) == "q" then
        local Q = Left:FindFirstChild("Q")
        local Q2 = Char:FindFirstChild("Q")
        if Q then
            Q:remove()
        end
        if Q2 then
            Q2:remove()
        end
    end
    if string.lower(Key) == "e" then
        local E = Right:FindFirstChild("E")
        local E2 = Char:FindFirstChild("E")
        if E then
            E:remove()
        end
        if E2 then
            E2:remove()
        end
    end
end)

Hope this helps you. :)