I don't remember what the setting number pertains to, but you still don't seem to be using the right calculation. First, if the entire lot, WITH HOUSE, is about 5000 sq. ft., you need to consider the lot size MINUS the area of the house, driveway, flowerbeds, etc.
If you take the actual area you covered, you will know how much you applied with the setting at 5.5. I would try, next time, setting it at about 1.5 and cover the lawn going both ways - small enough to repeat if needed as it is better to apply too little than too much. You may also want to avoid any fertilizer until your grass starts looking a little pale (not as deep green). A drop spreader might be better if you have hedges or flower beds that you don't want to throw herbicides into. Also, liquid herbicides or insecticides sometimes go on better with a hose-end sprayer, as you can hit only the areas that need it and you are done.