What should I do about the money I earned during my employment at the foreign company, knowing that I fell short in performing my work duties?

It is not permissible to breach the agreed-upon official working hours except with the permission of the authorized person. One must repent to Allah and return the value of the time not worked to the employer without informing them. This money can be deposited into the company's account or used to purchase goods for the company of equivalent value.