The periodic timer trigger (the second one) runs all the time. It should run only when the spell is casted.
For that, in trigger "start fire" have an action in the end "Trigger - Turn on (move arrow <gen>)" and the "move arrow" trigger, untick the "Initially on". By the way, there is also a point that should be variable-d. The point with the offset, in the periodic event "move arrow". (Point1 offset by 15.00, bla bla) is a new point to store in a variable.