size of pipe out of muffler, mine is 2 1/4'' and my resonator pipe is 2" I think it's the wrong muffler.

 

Exhaust system parts are usually mostly the same size among manufacturers, however, there are some that don't conform and if a complete system was installed by a non- conforming manufacturer, you either have the incorrect muffler or may need to use a muffler made by that particular manufacturer. It is not unusual to have to replace the entire system from the converter back to the end of the tailpipe.