Automatic gun code shooting multiple times?

I am trying to make an M4A1, an automatic gun, but the code that shoots the bullets will shoot bullets twice as fast if I double click and hold down on the second click. Why? Am I not setting variables correctly? Is there a different method of auto firing I should use?

Below is a video of the problem. The first half is shooting normally, the second is when I double click and hold:

https://www.youtube.com/watch?v=o-C6Krr9GkM&feature=youtu.be

And here is the code (Ignore commented out code):

mouse.Button1Down:connect(function()    
        mouseDown = true
        repeat
            if mouseDown and ammo.Value > 0 and not isReloading and player.Character.Humanoid.Health > 0 then
                ammo.Value = ammo.Value - 1             

--              if ADS then
--                  xOffset = aimOffset[math.random(1, #aimOffset)]
--                  yOffset = aimOffset[math.random(1, #aimOffset)]
--              elseif not ADS then
--                  xOffset = NoAimOffset[math.random(1, #NoAimOffset)]
--                  yOffset = NoAimOffset[math.random(1, #NoAimOffset)]
--              end
--              
--              local mousePoint = mouse.Hit.p
--              
--              local xRandomAxis = math.random(1, 2)
--              local yRandomAxis = math.random(1, 2)
--              
--              if xRandomAxis == 1 then
--                  xOffset = -xOffset
--              else
--                  xOffset = xOffset
--              end
--              
--              if yRandomAxis == 1 then
--                  yOffset = -yOffset
--              else
--                  yOffset = yOffset
--              end

                local ray = Ray.new(tool.Barrel.CFrame.p, (mousePoint + Vector3.new(xOffset, yOffset, 0) - tool.Barrel.CFrame.p).unit * 300)
                local part, position = workspace:FindPartOnRay(ray, player.Character, false, true)

                local beam = Instance.new("Part", workspace)
                beam.BrickColor = BrickColor.new("Dark stone grey")
                beam.FormFactor = "Custom"
                beam.Transparency = 0.5
                beam.Anchored = true
                beam.Locked = true
                beam.CanCollide = false

                local distance = (tool.Barrel.CFrame.p - position).magnitude
                beam.Size = Vector3.new(0.1, 0.1, distance)
                beam.CFrame = CFrame.new(tool.Barrel.CFrame.p, position) * CFrame.new(0, 0, -distance / 2)

                game:GetService("Debris"):AddItem(beam, 0.1)

                script.Parent.Shoot:Play()

--              if part then
--                  local humanoid = part.Parent:FindFirstChild("Humanoid")
--                   
--                  if not humanoid then
--                      humanoid = part.Parent.Parent:FindFirstChild("Humanoid")
--                  end
--                   
--                  if humanoid then
--                      player.PlayerGui.Hit:Play()
--                      humanoid:TakeDamage(7)
--                  end
--              end

                wait(0.2)
            else
                wait(0.2)
            end
        until mouseDown == false