This is how I understand the Perseverance of the elect in the TULIP.
If I am one of the elect, then I will persevere [by the grace of God, not of my own power] in a life of holiness, never ending up in unrepentant sin but ever confessing my sins and seeking to walk with God, until the time of my death.
But I haven't reached the time of my death yet, so I still have the potential, if I am not in fact of the elect but only think I am, of ending up in unrepentant sin. If I do end up in such a state and die, then I find out, finally, that I wasn't one of the elect to begin with, which is why I did not persevere.
Therefore, even though I think I'm one of the elect based on the fact that I believe the gospel and seek to please God and to strive against sin and confess it, I can never be 100% sure that I am an elect, until I die in a state of perseverance.
Therefore in Calvinism, I can never have 100% assurance of salvation [I didn't say "eternal security", I said "assurance of salvation"].
Is my understanding correct? If not, please explain why not. Thanks