Why can't I dash backwards?

The dash works fine in all directions except directly back when you're shift locking. Without shift locking, it works completely fine.

Any good solutions?

Local Script

local UIS = game:GetService("UserInputService")
local player = game:GetService("Players").LocalPlayer

local dashAnim = script:WaitForChild("Rolling")

--Settings
local key = Enum.KeyCode.Q
local velocity = 13000 -- Dash Speed
local debounce = false
local cooldown = 0.5
local duration = 0.22 -- Dash Duration


local function Dash()
	local character = player.Character
	if character and not debounce then
		debounce = true

		local humanoid = character:WaitForChild("Humanoid")
		local hrp = character:WaitForChild("HumanoidRootPart")

		local loadedDashAnim = humanoid:LoadAnimation(dashAnim)

		local dashDirection = nil
		local moveDirection = humanoid.MoveDirection
		local lookVector = hrp.CFrame.LookVector
		local minusVelocity = -velocity

		local onGround = humanoid.FloorMaterial ~= Enum.Material.Air and humanoid.FloorMaterial ~= Enum.Material.Water

		if onGround then
			if moveDirection == Vector3.new(0, 0, 0) then
				dashDirection = hrp.Position + Vector3.new(lookVector.X, 0, lookVector.Z)
			else
				dashDirection = hrp.Position + Vector3.new(moveDirection.X, 0, moveDirection.Z)
			end
			local bodyGyro = Instance.new("BodyGyro")
			bodyGyro.Parent = hrp
			bodyGyro.MaxTorque = Vector3.new(math.huge, math.huge, math.huge)
			bodyGyro.D = 0
			bodyGyro.P = 500000
			bodyGyro.CFrame = CFrame.lookAt(hrp.Position, dashDirection)

			local attachment = Instance.new("Attachment")
			attachment.Parent = hrp

			local vectorForce = Instance.new("VectorForce")
			vectorForce.Parent = hrp
			vectorForce.Attachment0 = attachment


			vectorForce.Force = Vector3.new(0, 0, minusVelocity)

			loadedDashAnim:Play()
			humanoid.AutoRotate = false

			wait(duration)

			humanoid.AutoRotate = true

			vectorForce:Destroy()
			bodyGyro:Destroy()
			attachment:Destroy()

			wait(duration)
			loadedDashAnim:Stop()			
		end

		wait(cooldown)
		debounce = false

	end
end