If you take this apart, you can see which holes are enlarged.

If only the holes in the flap are enlarged. you can put waehers under the rivet heads. If all the holes are enlarged, you can go to larger rivets and drill out the holes to fit, or use washers on both sides.

As was mentioned, proper-sized bolts or screws will work.

The only thing to watch for is getting all the holes to line up properly. When I changed my front bumper, I made sure the inner fender was attached properly (the nuts holding them to the chassis tend to get lost and the bumper sags) and I lined ALL the holes up with nails in them before I started to attach the rivets.

I installed the worst-fitting rivet first. If you don't do this, the alignment errors add up, the pieces are held in place, and the last hole may not line up at all.
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96 855R, 95 855,854, 90 744 Ti - 343,000 Volvo miles put on 7 bricks