The spec and the actual quantity you should put in can vary greatly. I have the same engine as Heron but I can only add about two gallons after draining the oil and changing the filter. Any more raises the level beyond the full mark on the dipstick.
I suggest adding a gallon and a half or so, waiting a few minutes and then checking the level with the dipstick. Add more oil a quart at a time until you see oil on the dipstick, then bring it up to the line. Start the engine and run it at idle for a few minutes. Shut it down, wait a few minutes and then bring the level up to the dipstick mark again.
Don't be alarmed that you will see no oil pressure for several seconds when you start the engine after an oil change. It takes that long to fill the filter and build pressure.