Sometimes buyers order me without contacting me before pleasing order, that why I cancel the order because I have no time to complete the new order because of my old client works.
Why should buyers message you before they order? Fiverr is designed for buyers to order any gig they want, when they want to.
If you don’t want any new orders, you can always pause your gig until you’re free.
You can also limit the number of orders that can be in queue. So set it to 3 or whatever you like and once you hit that threshold, no one else can order till you deliver one.