Very nice work on your cannon! It should provide plenty of fun and excitement.
I do not mean to be a naysayer, but safety is of the greatest importance here, and I would not go by that chart as it is for powder of a larger granule size, probably 1F judging from the curve shown there, possibly for 2F but I doubt it. That chart is also for grains of weight, which is a different measurement than grains of volume as is usually used for the F grades of powder. For the bore size that you have you should be using 1F, but you can get by with 3F if you use a smaller load. Remember that 3F will generate far greater pressures and will burn much faster than 2F or 1F. The smaller the granule size, the faster it burns.
As for caliber and how much powder to use, the general rule of thumb is as follows (measuring by volume):
Bore size less than .50, use 3F. Use 1/2 the caliber as a good place to start. (EX: Caliber is .44, start with 22 grains.)
Caliber of .50 to .70, use 2F. Use the caliber as a good place to start (EX: Caliber is .58, start with 28 grains)
Bores of .70 up to about 2" use 1F. Caliber times 1.5 is a good place to start (EX: Bore is 1", start with 150 grains
If I were you, I would start at 35 or 40 grains with 3F due to the diameter of the bore. That will be enough to make quite a show. Make sure you aren't standing behind it when it goes off. I definitely would not fire 100 grains of 3F out of that brass barrel, at least not without being behind some sort of shrapnel proof barrier.
You can fire a small charge from a muzzleloader (or cannon) hundreds of times, but you can fire too big a charge only once.