Is the feeling that acts of worship are not accepted by Allah Almighty considered a [satanic] whisper (waswas), and how can one get rid of it?

The fear that afflicts you during acts of worship is a sign of good, and it is a healthy anxiety that afflicts those for whom Allah intends good, for Allah Almighty says: (And those who give what they give while their hearts are trembling because they know that to their Lord they will return - It is those who hasten to good deeds, and they are the foremost in them). The Prophet, peace and blessings be upon him, explained the verse as referring to those who fast, pray, give charity, and fear that it will not be accepted from them. The believer combines excellence and apprehension, while the hypocrite combines wrongdoing and a sense of security. Therefore, you should perform acts of worship with perfection and hope for acceptance, and be optimistic about good.