[Generic, unwanted advice]: "Don't care too much, it's no big deal", "The outcome isn't important, it ain't the end of the world", "Just focus on putting your best foot forward, don't worry too much about the other person's expectations", "You'll see how unimportant all your worries and fears are once you actually do this", "STOP OVERTHINKING AND JUST *Insert Shia Labeouf Meme here*"
Yeah, uncertainties in the dance of romance suck. The above nuggets of crap are in my opinion completely valid and I hope you get some use out of them, but your main problem seems to be just nerves. Now, as for actual, concrete advice...
1. Trust the other person. If they're you're friend, and you're a good judge of character, they're in all probability not gonna overreact or be mean about any sort of advances you make, and that's if they're unwanted advances.
2. Talk yourself up. Just nothing but positive mental vibes, about anything and everything you're afraid of. Like an internal soundtrack of "I can do this", "It's gonna be fine", "It's just a movie". This is pretty generic advice, the key is just repetition, you have to force yourself to see yourself and the imminent reality of your movie outing in the most secure, comforting way possible.
As a corollary to this, don't try and think of the positive reinforcement you're gonna be saying to yourself as "forcing" yourself, or struggling or anything like that. Imagine you're a little babby child, being told something by your parent/best friend/most trusted figure, and you ACCEPT THE THING TOLD TO YOU AS THE GOSPEL TRUTH. We were all at a certain age where we would believe the world was flat because we couldn't and didn't feel the need to think otherwise, that's how susceptible you have to make yourself to your own positivity. HAVE FAITH in the things you are telling yourself, as if you weren't the one telling them
3. If you ever need a confidence booster, something to calm down, aside from the whole positivity talk and imagining your happy place and other reasonable stuff like that, do something physical. Do anything that makes you feel more secure as a living, powerful organism walking this Earth. As silly as this sounds, get a sword, or a club, or anything you feel would be an advantage in a melee fight, and just swing it around. Imagine yourself slaying whatever metaphorical dragons you have in your daily life, just REVEL in the feeling of power that comes with action and the illusion of invincibility.
An alternative is just physical exercise, doing something that you are really good and take pride in, anything to reaffirm to yourself, "I AM AN AWESOME HUMAN BEING"
Hope literally any of this helps, have fun on Saturday.