Zola is offering free shipping on all items. Are you offering free shipping on all items? If not, you're going to lose business to them. I advise you to offer free shipping and make less margin on the order vs lose the entire order to Zola.
In general, margins are smaller on online orders. This is well documented--and now accepted--as a business practice. Accept this fact and you'll survive and grow. Don't accept it and you'll lose orders and struggle online and likely fail.
This is our third post in two weeks about margins which have been increasingly in the news: