You have set yourself something of a challenge. It isn’t impossible, but as a first time you’ll need to build your confidence ahead of time, do as much prep as practical to inform the players so you’re not doing that in your tight slot of game time, and be prepared to have a little more fixed in place than you might otherwise to consider.
I ran Sunset Kills for a convention last year, having never run it before and it being my fourth attempt at a PbtA game. I’ve never really been comfortable with the way PbtA runs, but I’m always up for a challenge.
I knew what I wanted the finale to be, broadly - in that I knew what the evil in the town was trying to achieve - and I knew I wanted to start it - Kingston Falls thirty-five years after a night of destruction, revelry and murder than defied explanation.
The rest I left to the players, guiding the narrative, driving the soft moves, facing the hard ones when dice ran against them. I’m not convinced it was my best game ever, but we all enjoyed the creative process, I managed to keep the improvisational elements flowing, and we managed to create a memorable denouement in the town’s condemned communal swimming pool.
I wish you the best of luck. Keep up the pace, run with the players’ creative, and the best of luck to you.