You just need to set up your board creation event in a way, that it runs only when you want it.
Different examples of how you can do it:
1) add the trigger once while true condition
2) use a global, local or instance variable, set it as condition to be 0, and when creating the board set this variable to 1
3) put the generation event below a triggered event (those with the green arrow) - those only run on specific situations (i.e. on start of layout)
4) compare two values: boardsquare.count = 0: create board; = count the number of board squares present in the layout, if there are no board squares, it creates the board