Retrieval of uds

Dear Sir, I am an owner of 1 apartment in a building consisting of 2 shops and 10 apartments, in Visakhapatnam. All Sale Deeds were registered in 2009 / 2010 and the Occupancy Certificate was issued by GVMC in 2010. Apartment Owners' Association was formed in 2010. Recently during interaction with other co-owners, it was realised that the total of UDS mentioned in the all the Sale Deeds put together is less than the Plot Area. We just realised that the builder / land owner has retained his title on some portion of the land. Please guide how to get the same into our ownership. The builder or the land owner do not own any apartment / shop in this building.