What should I do about my constant feeling that my knowledge of Allah is incomplete, and my fear of a bad end and the non-acceptance of my deeds, despite my religious commitment and good deeds?

Fear of not having one's deeds accepted is a good thing, but one should not exaggerate it lest it lead to despair. To increase one's knowledge of God, one should ponder the Quran, reflect on God's creations, and study books of 'aqeedah (creed). A Muslim should worship his Lord with sincerity and perfection, hoping for the acceptance of his obedience. The righteous predecessors feared that their deeds would not be accepted and that they would have a bad ending, but there must also be hope for the acceptance of deeds, for fear and hope are like the two wings of a bird.