Hi, Vincent,
We need more data.
Are you determining the project size from the exported movie, or by some other way? When you say that you "deleted every other project and all media" what procedure did you follow to accomplish that?
The Get Info box in your screen shot shows that your library has 123.24 GB in it. The library size is comprised of your current project plus all other events,media, and projects contained in the library. Go to your Samsung drive and Control-click on the library's icon. In the drop down menu, click on Show Package Contents. The resulting folder that appears will display the projects and events and media that is in the library. What does it show? Is your current project the only one in there, or are there other events and projects in there?
Share your project to your desktop, using the Good Quality (not Best Quality --pro res) setting. After it finishes rendering, you should have an Mp4 movie on your desktop. Do a Control-click/Get Info on the movie's icon. What project size is shown in the Get Info box?
Before you share the project to your desktop, check to make sure that there aren't other clips, audio, and fragments of editing located down the timeline after what you consider the end of the movie. Expand out your timeline with the slider located above and to the right of the timeline to make your search easier. Delete any extraneous media that you find.
If your original clips were highly compressed that would reduce the file size. When exported by iMovie they may be exported in a much less compressed format, and possibly a higher bitrate, that would account for an increase in total size. Also, exporting at Best Quality (pro res) can result in significantly higher overall size, due to it higher bitrate and less compression.
-- Rich