You need to cut your strips 2.33 inches wide. If you haven't cut your snowballs yet, it might be easier to change their size than to try to cut in thirds when rulers are marked in quarters. If your snowballs are 6.5 inches, then your strips can be 2.5 inches. Three strip block will have 2 seams, not one, so you need to add one inch. This block will finish at 6 inches.
If you decide to go with 2.33, put two pieces of tape on the ruler once you determine where 2.33 is. Saves trying to find it again and again.