Visitors to the new Marble Arch Mound are being offered refunds due to “teething problems” with the attraction.
The authority said it is working to resolve issues “over the next few days”.
Anyone who booked a ticket for the first week will be contacted and offered a refund as well as a free return ticket “so they can see the mound at its best”, the council said.
It is part of a scheme to increase footfall in the shopping district as lockdown restrictions ease.
We are aware that elements of the Marble Arch Mound are not yet ready for visitors
But there have been some complaints following its opening that work is still ongoing, with some people taking to social media to pan the attraction.
In a statement, Westminster Council said: “We are aware that elements of the Marble Arch Mound are not yet ready for visitors.
“We are working hard to resolve this over the next few days.
“In light of the delay, we are offering anybody who has booked a visit during the first week a return ticket free of charge so that they can enjoy the full experience including the Lightfield art installation, M&S Food, and the landscape once it has had time to bed in and grow.
“People who visited the mound today, and people who are booked for the rest of the week (including the weekend), will be contacted and offered a refund and a free return ticket so they can see the mound at its best.
“Anyone who has booked a visit this week can go up the mound as planned and then still take advantage of the free return ticket.
“The mound is a living building by design.
“We’ll continue to adapt and improve London’s newest outdoor attraction and resolve any teething problems as they emerge.
“We’re sorry for the delay and look forward to welcoming visitors when they’re ready to enjoy all the mound has to offer.”