If I memorize the Qur’an and then forget some of its verses and pass away, what will be the fate of those forgotten verses, and will my parents be crowned with the crown of honor despite my forgetting some of them?

It is mentioned regarding the virtue of one who recites the Qur’an and acts upon it that their parents will be adorned with a crown on the Day of Resurrection. This virtue applies to the preserver (hafiz) of the Qur’an, not merely the reciter. If someone memorizes the Qur’an and then forgets some verses, if their forgetfulness is not due to negligence (such as due to illness or old age), then they are hoped to receive the reward of the preserver of the Qur’an, based on the Almighty’s saying: ﴿Indeed, those who have believed and done righteous deeds – indeed, We will not allow to be lost the reward of any who did well in deeds.﴾ [Al-Kahf: 30]. However, if their forgetfulness is due to neglect and carelessness, they may miss out on the virtue of the preserver, because the encouragement to memorize the Qur’an includes continuous companionship with it through recitation and action, and not abandoning it after memorization.