Unable to make changes in checkout page due to checkout is disable message

i am unable to edit actual checkout page when i try to open check out page it opens a sample checkout page

and this message appears on top which is

"You are designing a sample checkout page. We're in the process of rolling out a new experience for checkout, and changes you make may not appear to all shoppers during the rollout. Checkout is disabled."

i want to add a "continue shopping" button in checkout page is there any way to make changes either through custom code or through any other way please do let me know

is there any way to show "continue button" all the time in "add to cart "page even if there are items added to the cart ? 

Does anyone know what they are doing and why we cannot make changes? I cannot seem to find any detail about what is being done to improve the checkout page nor when it will be ready.