problem with item or GUI?

good to everyone, I'm new to mcreator and I've been watching tutorials and stuff. What I need helps is that when I make a backpack with blockbench, (I think there is no problem with blockbench) if not when I do the GUI or in the same item since when I make the item with inventory:
1. do not open or right click
2. I put a procedure that I saw here and if it opens
3. After putting the procedure, when I put the items inside the item with inventory, when I close it, the items come out.
help please I'm new XD