Land border disputes

Dear Sir , Now I am in a situation where I need legal advice from you on my land boarder . 50 years back my father gave half of his house to my sister as gift .He executed the gift deed which says the 1.5 cent of total 3 cent has been given as gift .Only the direction is mentioned for the 1.5 cent area in deed which means the half from south side of the house no other border details are mentioned in the deed . Since the house is built as single one the common wall doesn't devide the house equally because of this my sister is living in 1.3 cent house area and my portion size is 1.9 (actual house size is 3.2 but gift deed mentioned only 3 cent as total size ) .FMB map record in taluk office also shows the land area as 1.9 and 1.3 area(same as the house area for both). 10 years back I got the remaining portion of the house from father's will .My property document also created based on the house area which is 1.9 .I see a statement in my document which says eventhough the size should be 1.5 cent the the current living area of 1.9 cent is considered as the asset area for this property. Now my sister is making issue with border since her house is having less area than the area specified in the gift. I don't know what is the legal way to fix this . My property document and the FMB map record in taluk is matching the land area.but for my syster it is not