The prel file is the project file. You need to export your Timeline content using the Share section options.
Please see Share whose major categories are
Mobile Players and Phones
For what you want to do, click on Computer where there are still more choices.
You may not see all the choices so use the thin scroll bar to the right of the choices to scroll
down to the one you want.
Please let us know what type of project you have 4:3 or 16:9, SD or HD.
If HD, look at the Presets = MP4 H.264 1920 x 1080p30 (if you are in the United States).
We can discuss exact export settings once we know
a. your project settings
b. the properties of the video on your Timeline
Please review and consider. We will clarify as needed.