How can you lose it when you didn't do anything to earn it. It was done when Jesus died for you. You either believe it or not. It is a gift. Would you be insulted if you gave a gift to someone and they tried to pay you for it? What do you think God thinks when he sees someone actually thinking they could add to the most wonderful gift ever given?
You're saying that you can't lose a gift? Sorry - if that's a serious question, we have no common ground for discussion.
Our salvation is not a gift and yet it is. It is ours at Baptism, but some people blow it by committing sin and not repenting. They lose their gift! And we can lose it too if we don't repent!
OSAS doesn't work for Christ. He will judge us all according to how we lived our lives.