Hi, @Renay.
Don't worry, especially if this is to be an ongoing thing for you and your organization. You'll have plenty of opportunities to "up your game" as time goes on. I've been facilitating Zoom Meeting and Webinars for about 4 years now.
It seems like you might be working with attendees who are known to you and/or your organization, and hopefully are friendly and polite. That will help tremendously, knowing that you shouldn't also have to worry about "crowd control" too much. There's always someone who forgets to mute themselves; as the Host, you can mute everyone as needed.
On the ... menu of your Participants window, I'd recommend initially enabling the Mute Participants upon Entry option and disabling the Allow Participants to Unmute Themselves. This will allow you to control the amount of "chatter" that goes on during the film. You can enable the Allow Participants to Unmute Themselves option as you think prudent, but when it's time for the film, disable it and make sure everyone is muted.

As the host, tell everyone that they can select the Standard View mode, and if all cameras are off, no one will be visible while the film is playing:

We normally have an hour of discussion after the film showing, with 4 panelists. Not sure if you will have some discussion after your film, but use your judgement on whether you let the conversation flow freely vs. taking a controlled approach. If you briefly mention how you intend for it to work, in most situations, people will respect your announcement.
After the film is over and you've stopped Share Screen, you can use Spotlighting to control which people are shown for those that select Speaker View. You can spotlight multiple people if their cameras are on.
If something doesn't do quite right, don't worry. Stay calm. "Fix" whatever doesn't seem to be right, and move on. You'll get more confident and learn some new techniques along the way! "Fake it til you make it" is good advice.
Reflect on how it went, jot down some notes, and come back here later and let me know how it went. In a few days, I'll reach out with a PM (private message) and we can discuss in a Zoom call if you like.
Good luck!