Load and unload the magazine 10 times with 6 rounds. I'll bet on the 11th time the last round will go more easily. In my experience the LC9s mag. spring is stiff when new. That's actually a good thing over the long term but loading the last round can be a fight when it's all brand new. Push the follower down on the 6th round and make sure that it's not binding. If that fails, report back. Maybe the spring or follower are bound up somewhere. It's not hard to disassemble the magazine to inspect the spring, follower and inside of the magazine but do that as a last resort.
When the magazine is fully loaded with 7 rounds, even with a closed, locked bolt the magazine should "snick" into place with thumb pressure and not have to be hammered or whacked into place.