If it's only the side setting triangles that are like that, I would probably take them out and cut new ones, or cut these down to correct size before piecing them back in. Alternatively, you can try un-sewing just one edge. Then fold over the excess into that seam, iron, trim, and sew just that one side back in.
If you still have some excess fabric in the edge when you layer, you can run a gathering stitch along each edge. Pull up the gathering stitches as needed to evenly ease the fabric. If it's not too much, you will be able to eliminate most of the puckers. You could do the same thing with the top as is in the photo; in that case you will have puckers in the edge, but at least they will be evenly distributed puckers!