Agreement of Sale with Builder flat.

Now get a rectification deed to the AOS mentioned the period as mutually agreed between you and builder.

An agreement Of sale can be enforced within the period mentioned in it or where time period to perform contract is not mentioned then agreement can be enforced within three years from date of its execution or three years from denial to perform contract in limitation period.you may insist  builder to perform contract  within three years .

When did you execute the agreement to sell ?

It is valid for 3 years, if not mentioned.

Consult and engage a local prudent lawyer for professional guidance and necessary proceeding.