We are starting a Sprint today, first day of a 3 week Sprint. Our requirements from the client are still evolving, so remaining hours is estimated on some unclear values.

 How should a deviation in overall design be managed in scrum. For example, a requirement, covered in this Sprint, changes, drastically changing a estimate. Causing the Sprint to land up days behind time. Are we still committed to all the work? We are supposed to be agile. Our do Sprint items get moved out to accommodate the change? 

 advice would be most useful.