"The problem with this script is that when the alarm turns off, the lights do not return back to their original brightness of 3. How can this script be fixed?"

The issue lies in the restoreLights function. The while loop is not correctly increasing the brightness of the lights. Here's the corrected script:

```lua
-- New function to gradually return the lights back to their original state
local function restoreLights()
	for _, part in ipairs(lights) do
		local light = part:FindFirstChildWhichIsA('Light') -- find the light within the part
		if light then -- make sure the light was found before proceeding
			while light.Brightness < 3 do -- while the brightness is less than 3
				light.Brightness = light.Brightness + 0.1 -- increase the brightness by 0.1
				task.wait(0.1) -- wait for 0.1 seconds
			end
			while light.Color ~= originalColors[light] do -- while the color is not the original color
				light.Color = light.Color:Lerp(originalColors[light], 0.1) -- gradually change the color back to its original color
				task.wait(0.1) -- wait for 0.1 seconds
			end
		end
	end
end

-- Call the restoreLights function after the alarm stops
alarm.Stopped:Connect(restoreLights)
```

The line `light.Brightness = light.Brightness   0.1` was changed to `light.Brightness = light.Brightness + 0.1` to correctly increase the brightness.