Muffler fell off tractor.......?

It is a cub cadet lawn mower. The screws came out and I could not match the size, so I jerry rigged it with ply-able metal string. It held up fine for todays mowing job. Very expensive to buy a replacement muffler. As long as this holds, is there any reason to worry? There are two exhaust pipes and the mufflers fits over both of them. It seems fine like this, but I know next to nothing about the workings of the combustible engine. It is a snug fit and is well in place, no different then if I would have used screws to secure it. Any help or advice would be greatly appreciated.