A regular 20-something year old woman is accidentally dragged in to a crime circle after she is mistaken for a professional hit(wo)man.

Interesting premise for a plot But not yet a plot . And loglines are about plots, not premises. So it needs fleshing out.

Unable to persuade a ruthless mobster that she is not a professional assassin, a woman must do X or else Y.

What is the X --the objective goal? What is the Y --the stakes if she doesn't?

That sounds like a very promising starting point, I can picture a lot of scenes that might come from that, well done. What genre do you plan that to be in? I can imagine it a confusion comedy, action thriller, gangster drama or all of that combined. :D (I personally would hope for all of that combined as a viewer, I think.)

Thank you! :) The idea is that she would have to 'play the part' (while trying to no actually kill anyone) as a way to, as safely as possible, get herself out of the situation