Attempting to create a DUPLICATION mod for future versions that stuck on 1.12.2

Hello, I am trying to create a block where you right click it, it gives you another of the block in your main hand. The interval is meant to start of going up by one each time for this block. When I try this procedure, it doesn't go up by one, and when I remember the item in hand + 1 it stays stuck as 2 for some reason.

Any suggestions?