Massallah pertaining to missing Rakaahs

Assalamualaykum Mufti,
After missing 2 Rakaats Witr Salaah,I joined in the 3rd Rakaat reading Dua e Qunoot with th Imaam and thereafter stood and read my missed Rakaats(as in Fardh)Is this permissible or must one read Witr on their own if Rakaats are missed
Jazakallah