What is the solution to the problem of feeling guilty when adhering to the prescribed number of tasbih and dhikr, while rejecting the suggested increase in those remembrances, and is this considered a rejection of good?

You are not sinful for what you mentioned, as it is from self-talk (hadith (definition) al-nafs), which has no consequences. The Prophet (peace and blessings be upon him) said: "Indeed, Allah has forgiven my nation for whatever thoughts occur to their minds, as long as they do not act upon them or speak of them." You must cast off these thoughts and illusions and not allow Satan a way to you. Occupy yourself with remembrance (dhikr) and glorification (tasbih).