Mistake In Salah – I Did Not Pay Salam Properly
If you had turned your face and said السَّلاُمُ عَلَيكُمْ وَ رَحْمَتُ اللهِ then you have fulfilled the obligatory part of Salah so your prayer is valid. But if you had missed any of the part then you can perform Sajda-e-Sehaw. Please see for details : Discussion 62524
Actually, I said ‘Assalamu alaikum warahmatullah’. But, did not turn my face properly. i.e turned my face straight, before completing the full sentence (assalamu alaikum wa rahmatullah).