Seems like I have cut them off before, too. Even when I didn't, seems like they got pull off trying to get them through the holes.
I guess the 2 options are a misformed pan, or bad gaskets. Since you have tried two gaskets, sounds like the pan might be the issue?
Did you try pushing the pan down? Not suck it down using the bolts, just put some weight on it to see if the gasket would squish and make things fit?