Is it permissible to retract the sale of a gifted plot of land, bestowed by the ruler as a grant and endowment, which has not yet been allocated and for which the title deed has not yet been received, due to an urgent need for it and its rising market value, especially since the sale has been made and the price received?

Selling land before it is allocated and its ownership is transferred is not permissible, due to the inability to deliver it and because it has not yet entered into the seller's possession. This falls under the category of selling what one does not possess, which is prohibited. Sheikh Ibn Baz also issued a fatwa (definition) stating that selling land grants before acquiring and receiving them is impermissible because it involves gharar (definition) (uncertainty/risk). Therefore, this sale of yours is void, and you must return the money to the buyer. If you acquire possession of the land later, then there is no harm in selling it at that time.