You've almost figured everything out yourself.
Move "Show save dialog" to event 240, and remove "Wait for previous action to complete".
Now look at the "Write text" action. You need to write saved data SaveStateJSON into the file with filename NWJS.ChoosenPath
What you are currently doing is you are writing chosen path into the file named "mysave". Why?
It looks like you are trying different random things in hope that one of them will work, instead of taking a moment to read. I mean it's right there - Path, Contents. You don't need to be a programmer to know what path and contents is.