3.2/gallon is just 40 to 1 ratio. If you were to put 4 oz it wont hurt anything. Chances are that 3 oz to a gallon wont hurt either. If you only have 3 oz only add .94 gallons of gas to three ounces which would also be 40/1.
I keep a tiny container marked with a sharpie incase I want to use "bulk" 2 stroke oil for my weed eater/chain saw. I actually demonstrate how lazy I can be and buy the small 6 packs.
