Have you removed your paper yet? Sometimes, because I use cheap paper - the paper can distort before removal. While removing the paper, you can also stretch your seams and fabric if you pull really hard to remove the paper. I use a small stitch and because I use cheap copy paper, when removing it, I run a damp qtip down the stitches which softens the paper under the stitches and the paper removes easily.
I trim each seam as I go and press every piece that I sew onto a pp project carefully. This eliminates any unwanted fullness. I rarely have a wrinkling issue.