Next, stitch your upper collar to your under collar, right sides together. Trim and grade your seam allowances so that the seam allowance closer to the upper collar is the wider seam allowance.
Now, baste the raw neckline edges of the collar together. Your raw edges may not match up perfectly anymore due to the turn of cloth, and that's okay. Trim off any excess if needed.
If you've moved ahead, now would be a good time to start assembling your lining. As always, let me know if you have questions!