You are entitled to a UDS to the extent of 600 sq ft which would be mentioned in your sale deed,  if it is not mentioned then you may go for a rectification deed. 

Yes you may require rectification deed in above case

Deed of rectification can be executed to rectify mistake in sale deed 

it can mention your divided share in land and exact boundaries of 600 square feet of land 

Any flat-owner is legally entitled only to an undivided share of the land over which the construction stands, in proportion to the built-up area of the flat. No one can claim a divided share. Moreover, the entire land extent of 2,400 sft. cannot be equally divided among the 4 flat-owners at 600 sft. of undivided share each. The area of construction over the common area, such as walls, has to be excluded from the total extent of land. Request your builder to explain the rule to your banker!

- As per rule, when a person buy an apartment then technically he buys two things,

1. First is the constructed part of the building where that purchaser after becoming owner will actually reside, and

2. The Second is a proportionate share of the land on which the property is built, and this share of land allotted to the flat buyer is known as an undivided land share or  .

- Further, the sum of all the undivided shares for each flat owner must be proportionate to the area of the land in which the apartment has been constructed.

- Since, the 4 houses are of 600 sqft , but as your documents showing more than this UDS , then you may face problem in future , and hence you can rectified the said error after executing a rectification deed. 

Since original sale deed does not mention boundaries of your plot Deed of rectification has to be executed to mention boundaries of your plot 

It is better to mention all the facts correctly at the first instance itself. Sub-division refers to survey no. in Revenue records. For eg. a land in the original Survey No. 123 if sub-divided into 4 parts becomes 123/1, 123/2, 123/3 and 123/4 subsequently. If the promoter has sold you a piece of land admeasuring 600 sft., out of the total extent of 2,400 sft., with metes and bounds, the boundaries and the dimensions of the plot need to be mentioned in the sale deed clearly. For eg., bounded on the North by, South by.....etc., and admeasuring x ft. East-West on the North, y ft. East-West on the South .....etc., in the Schedule of the Property in the sale deed. In your case, a rectification deed needs to be executed and registered to correct the omission.

Yes you can do the aforesaid

When the entire parcel of 2,400 sft is equally divided among 4 buyers, you cannot call it UDS. The use of the term UDS causes confusion. Please state all the facts correctly to get a proper advice.

Since you were the first buyer, probably the seller would not have demarcated and sub-divided the land to you, however it was your duty to sub-divide the vacant land and after that you should have constructed the structure over the vacant land within the schedule of property that you had purchased.

Even now you can apply for sub-division of your property from the main property on the  basis of the registered sale deed in your favor in which there will be a mention about the schedule of property that you bought.

If need be you may get a registered rectification deed to prove the actual extent of the proeprty that you purchased, in fact you are the absolute owner with clear and marketable title to the land below your building which cannot be disputed by anyone just because there is a mention  in your registered sale deed that it is an UDS.