Hi,
You didn't say what method you were using to do the resizing. I am using an earlier version of iMovie 10 so not specifically familiar with the one you are using. In my earlier version, the resizing is done by doing the following:
To resize the project window, put your cursor on the border between the timeline and the viewer (i.e., the top edge of the gray area). When the cursor morphs, drag the edge up or down. That will automatically resize the browser and viewer.
Clip display sizes are adjusted by clicking on the Settings button located above and to the right of the timeline, and adjusting the clip display size with the slider in the Settings box. Also, you can adjust the size of the clips display in the timeline by using the slider that is located just to the left of the settings button, that zooms the timeline display bigger and larger.
-- Rich