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