Hi Gina! I can help you. Your going to cut the sleeve piece. Fold it RST so the smallest (c shape) is lined up and just stitch the C Shape.
Now, lay it in front of you so the C shape is on your right and the fold is on your left. It’s still RST.
What you have is a tube. Fold is on the left. C shape on the right. Open on top and bottom. RST still.
Your almost done! Take the TOP LAYER ONLY, (the fabric closest to the ceiling) and fold it UP onto itself WST(WRONG sides together)matching the raw edges. Pin it.
Turn the whole thing over and do the same to the other side. Bringing bottom edge up to the top, pin.
Now looking down at it… You have a tube with your raw edges pinned at the top. Fold is at the bottom. Right side are out and wrong side is in.
Attach sleeve as you normally would.