Add a "C", I am what has been,
Add a "G", I might be a queen,
Add a "P", I'll turn away from sin
Add an "L" and I may just give in.
This is a Reverse Hangman puzzle, see here for an example.
The final answer will be a string with one letter blank which can be filled in in several different ways to form a valid word (e.g, "_at" can make bat, cat, fat, hat, etc).
In your answer, please give the string with the missing letter and explain each line.