When your fermenter is empty, check the volume using known measured volumes. From your ingredients you will get 45 points/lb of DME (=135), 36 points/lb LME (=119), and about 28 points from a pound of grain. Total = 282 points. At 1.064 this equals a little under 4.5 gallons.
My numbers could be off slightly, but not much, it's conceivable you could have slightly over 4.5 gallons with a 1.064 wort and these ingredients.
I have 3 identical fermenters from 25 years ago. About 10 years ago I decided to check the volumes, and found all 3 read high; that is, at the 5 gallon mark, all 3 were actually only slightly over 4.5 gallons. I have re-marked them with permanent marker.