Is a customer obligated to pay an increase in price after an agreement has been reached, and what is the ruling on the small increase I took?

The questioner did not mention the nature of the contract. If it is a manufacturing contract (Istisna'), then it is permissible to revoke it because it is a non-binding contract before the work begins. However, after the completion of the work and the manufacturer's option to revoke has expired, it is not permissible. If it is a combination of lease (Ijarah) and sale in one contract, which is permissible according to the majority of scholars, then this is a binding contract that must be adhered to, based on the words of Allah Almighty: "O you who have believed, fulfill [all] contracts." It is permissible to request rescission (Iqalah), which is the termination of the contract by mutual consent of both parties. If the other contracting party accepts, then that is permissible; otherwise, the contract must be fulfilled.