I'm going to renege on a commission
why do you want to go back on your promise?
I was really scared when I found out that I had to produce 2000 pieces in 3 days.
It is bad to take on more than you can handle. You should try to make the deadline if you can but be honest with the customer.
Whatever. I'm cancelling the order.
You should talk to your customer and explain your situation and maybe they'll understand it. Try to find some way out instead of cancelling an entire order, it's gonna harm your business. From next time make sure if you can fulfill the order and try to avoid those which you cannot do in time.