The trailer comes before the movie

Not the other way around. In fact, you’ll never watch a trailer coming after the movie is released. And that, as they say, is that.
At Hollywood they know it pretty well. If they don’t start the communication strategy before they develop the product, they’re doomed.
Most startups fail because they don’t generate enough attention through a trailer.
Gabriel Weinberg and Justin Mares make that quite clear in their book Traction. In their own words: “Having a product or service that your early customers love, but having no clear way to get more traction is a major problem. To solve this problem, spend your time constructing your product or service and testing traction channels in parallel. Use the 50 % rule: spend 50 % of your time on product and 50 % on traction.”
Launching a movie is more about the communication than creating it. But, don’t get me wrong here. You should only create good trailers. The communication is as important as the product. Nonetheless, it doesn’t matter how much noise you generate around your product, because in the end, if your product’s not worth it, that’s what you get, noise.
No movie ever–worth talking about–was released without making a good communication before they got the product.
Don’t wait until the product is perfect. By that time, it’ll be too late.
Go. Make a great trailer and elevate people’s expectations. Because when you’re about to launch it people will be eager to buy from you.