From what you describe, you are done. No return policy here unless you were NOT the legal owner of the property and sold it fraudulently. The buyers have the ability to have many people involved in a transaction. Their agent, hids broker, inspector, lender, title company, insurance rep etc.
They closing agent always asks each party if this is their free act and deed and waits for a serious response.
Once the deed passes across the table, your done unless an illegal activity has occurred.