All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The majority of scholars are of the view that the second Tasleem in the Prayer is not obligatory, unlike an opinion of the Hanbalis. An-Nawawi said in Al-Majmoo’:
According to our Madh'hab, one Tasleem is obligatory and the second is not, which is also the opinion of the majority of the scholars.
An-Nawawi said in Al-Majmoo’ while talking about Tasleem at the end of the Prayer: “The minimum requirement is to say, “As-Salamu 'Alaykum.””
Ibn Qudaamah, Al-Hanbali said in Al-Mughni: “If he says: “As-Salamu Alaykum” and does not add any other words, then it is sufficient according to Imam Ahmed's statement.”
Therefore, if you meant that you said: After the first Tasleem, “As-Salamu 'Alaykum wa rahmatullah”, and did not utter the letter “H” of “Allah”, then this omission does not affect the validity of your Prayer, because it was completed with the first Tasleem. Therefore, you do not have to prostrate for forgetfulness, your Prayer is valid, and you are not required to repeat the Prayer.
Allah knows best.