Q: If i make one sajdah instead of two sajdah, what do  I do? Would sajdah sahw be sufficient?

A: If one sajdah was performed instead of two sajdahs, then in the following rakat, merely perform three . Thereafter, perform sajdah sahw.

If there was no rakat after the rakat in which you only performed one sajdah (instead of two) then merely repeat the salah again.

Allah Certainly knows Best