Unfortunately there's no way to scroll. Fuse wasn't designed to use so many different categories as we hadn't fully worked out the shared custom content story yet. Definitely something we can address in the future.
I would recommend merging similar categories. For example, merging "Armor (Boot)" into "Shoes" and "Armor (Chest)" into "Tops", etc. For each piece of content in the custom categories right-click on the icon and edit the custom content piece. You can switch categories and names there for any custom content.