Yes you can lose grace.....this is one doctrine I have do idea how it came to be or how any serious student of the Bible could believe it.
From start to finish in the Bible, old Covenant, and New, there are people who are saved, then lose it.
Just think of the Israelites in the desert. St. Paul warns us that what happened to them is a warning for us, not just a nice story to watch with the kids on tv each Easter time.
God saved the people from Pharoah through the Red Sea (St. Paul says this prefigures Baptism). They are saved from pharoah symbolizing Satan from that time and were no longer slaves.
They wander through the desert (symbolizing the desert of this life) but those who turn away from God are destroyed and die in the wilderness.
Only those who remain faithful enter the promised land (heaven).
Scripture explicitly states that this is the model for the Christian life in 1 Cor 10:1-13.
So if they could lose it, so can we.....this is mirrored in about a billion other versus, so once saved always saved is bunk...a tradition of men who want it easy and an excuse to sin.