You could probably visit your local muffler shop and ask them to expand your baffle a bit until it's a tight fit in the canister, it should take a tech about 2 minutes to do that. They use a mandrel slipped inside the diameter of the pipe and hydraulic force to shape the metal. There is a manual tool that you could do the same thing mechanically, but that may be the only time you ever use it, and most of those mechanical one's I've seen are for the exhaust tubing, and not the larger diameter of a motorcycle canister. Of course, if it's the oval canister, this entire expansion method wouldn't apply.
Another way to increase the size of the diameter would be to lay a bead of weld onto the edge/ends and then 'dress' it until you got the tight fit.
If you did this, you would have a spare, or a part you could sell on here, if someone needed a crash replacement part.
