Can only see half of folder screen?
View → Show Preview ⇧⌘P / Hide Preview ⇧⌘P toggles the pane on the right.
You can alternatively…

drag the edge of the window right to make the window bigger so you can see more contents without hiding the preview pane.
choose View → Arrange By to choose an arrangement of items — any arrangement will automatically place the folder contents within the view with only vertical scrolling.