If I accept Acts 22:16 KJV as the Gospel unto salvation, what lack I?

Only one thing: Remember to keep calling on the name of the Lord throughout your life and during your relationship with Jesus.

Call on Jesus to help you read and understand the Bible

Call on Jesus when you need help to do the right thing.

Call on Jesus when you confess your sins.

Call on Jesus just to give him thanks.

After belief and baptism, all that remains is relationship. If you remember to call upon the name of the Lord and heed is word you will be called, chosen, and faithful.

Romans 10:13 KJV says, For whosoever shall call upon the name of the Lord shall be saved.