You will need to specify a few things in your widget in order for the microflows it executes to respond to close form.
1) 'mendix.addon._Scriptable'.
2) run this in your postCreate: this.offerInterfaces(["close"]);
3) add this function in your widget: close : function() { this.disposeContent(); }
You can set your own instead of the disposeContent(), which will close the current form.
You also might need to add 'caller : this' to your execute microflow arguments if you don't already have it.