[aliceingoogs]

Wa ´alaykum as-salam wa rahmatu'Allahi Ta´ala wa barakatuh,

Congratulations on completing such a blessed task, sayyidi. Since no one has replied I decided to state the obvious... revision!
Lack of revision is probablt the most common cause of forgetting, whether it is memorization or understanding. If possible, you should try to to teach it, even if just to your friends. If not, you can practice by narrating and explaining it to yourself.

Wa Allahu a´lam.

wassalam