1.1 is a little low, beersmith shows the style at 1.5 to 2.3 vols
at 68*F, beer smith says add 1.71 oz for 1.5 vols
at 68*F, beer smith says add 3.86 oz for 2.3 vols
personally, i'd shoot for 2.3 volumes, i like well carbed beers.
and i'd definitely get a scale if at all possible, one person's 1/2 cup almost always weighs different from another's. you can get a scale pretty cheap at wally or target.