Loretta, you might use a bit of spray starch to have it lay properly. Are you sure that it is totally on grain as that would make it wonky? I've sewn with chiffon before & I always have fused the seam allowances with a light weight interfacing, used a longer stitch, & pressed carefully with a press cloth. I also lay it on tissue gridded pattern paper to prevent slippage when cutting. Now, that you have completed the jacket, other than adding some starch to give it a little bit of stability, I don't know what else to advise you to do. Sorry!
Marty
Brighten each corner where you are ... smile!