What you have right now is 1 BP for every instance of a gem. That means that every gem will be positioned at the exact same spot when you pick it up. What you need is to add some offset that tells the gems that they have to be placed behind your character + the offset.
You can do that in several ways. For example you can have a static variable inside your BP that represents your offset. You can then adjust it when you pick up a gem and when you “drop it”. If you don’t want to use static variables, you could maybe store the offset inside your character’s BP and access/modify it every time you pick/drop a gem.