I worked on my team's cannon a lot and our website has a lot of good information that you can use for ideas.
https://www.team254.com/shockwave/
The distance the shirt will be fired can be changed dramatically by how you roll up the shirt and if you add rubber bands not. For short shots we roll them up loosely so they open up almost immediately after leaving the barrel, another is to roll it up and add a single rubber band at the back of the shirt to hold it together in flight but after firing the front of the shirt will mushroom out to slow it down and for long shots we add two rubber bands on the shirt, one on the front and one at the back. Another way to adjust distance is to change the amount of time that you leave the valve open.