Doing %arg% with 1 argument will work the same, the slash character in aliases is not needed, and doing the slash character in the first line is also not needed. The skript wont stop itself either since the skript itself IS a loop, executing the same command every 3 seconds.
To stop this, you could use a variable and make another command to set that variable true/false. Then after it waits 3 seconds, check if said variable is true.