Teams often thinks they need to improve on estimating.
I think it is waste to try do that. 
But difference in actual and estimated velocity is good information, and nothing to be sorry about.
Mike Cohn have taught me this through his books "Agile Estimating and Planning" and "User Stories Applied". 
His teaching has been one of the most influental for me.
Find out more at his site: www.mountaingoatsoftware.com