I can't count the number of filmmakers who have asked me "why doesn't my exported image look like the one I shot?" Getting that question from my students is not only expected but encouraged. Getting it from people who've been making movies for five years or more is a bit discouraging.
Anyway, here's why your image doesn't look right: it's called workflow.
Before you go into production on anything, start with a camera test using the EXACT camera you will use in production (I'm assuming an HD shoot for the rest of this post). Write down your settings for resolution, frame rate, etc. All of them. Write them down. With a pen.
Shoot something simple then get those images into your editing system. That system will need to know the settings at which you shot. Go get that pen and paper thing with your settings and use those to set up your timeline for editing.
Put your footage on a timeline and export it using the exact same settings at which you shot. Same ones. Exactly. Take that high-res export and put it on a Blu-ray disc. Get that Blu-ray projected onto a screen. That image should look exactly like the one you shot (if it doesn't, you may want to check the projector. Otherwise, it should look exactly like what you shot).
Now, if you want differences (color correction, changes in resolution or frame rate for effect, etc.), you can test that, too. The idea is to get the image you want on the screen from a test. Then, duplicate that testing scenario in production.
Remember, your settings in production rule the day. Every adjustment you make subsequently should be derived from those settings.
To avoid future mishaps with image quality, simply hire people who know this process forward and backward. You might be the creative force behind the project, but that doesn't mean you know the equipment. There's no shame in letting a collaborator be the expert on the technology, especially if it gets you the image quality you want.