Declaration Deed

Last month I bought a plot of land in Kolkata.,West Bengal. But unfortunately in Sale Deed there remains two mistakes. On the page which have map of land Mouza mentioned is wrong again length of land is shown in map as 50 feet insted of 50 feet 6 inches. Now registrar has suggested us to make a declaration deed. I want to know the validity and importance of the declaration deed. Is it ok or there is a better way. Kindly give your valuable suggestion.