I'm replacing an OEM donut gasket at the rear of my car and its not fitting correctly.

I'm installing an aftermarket muffler on my car. The old donut gasket located between the muffler and the pipe from the resonator. The aftermarket muffler has the correct OEM flange on it. When I went to replace the old gasket the new gasket doesn't sit flush against the male flange that comes from the resonator. The original spring bolts are too short now as well. I tried to clean the flange from the resonator as much as possible and the gasket still doesn't sit flush. There's about a 1/8-1/4" gap. From videos that I saw the gasket is suppose to be tight against the flange and pretty tight I'm general. What do you think could be causing this issue and is there any quick solution for this?