Will a curse befall me if I speak about something I believe to be true or false without intending to lie, and someone curses me, saying I am a liar, knowing that I have asked for their forgiveness but they have not forgiven me?

What the person did by cursing you if you are a liar is unlawful, because it is not permissible to curse a specific person even if they are a sinner. And no sin will befall you as long as you did not intentionally lie, and the curse does not affect you because you do not deserve it.