Not being able to forget his sins is spoken of as if they were always in front of him where he can see them. AT: "I am always aware of my sins" or "I cannot forget my sins" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The word "sight" here represents judgment. Yahweh saw and did not approve of David's actions. AT: "what you judge to be evil" or "what you consider to be evil" (See: [[rc://en/ta/man/translate/figs-metaphor]])