Many felting projects use the washing machine, but the relatively small size of the piece makes it tricky and it also gives you less control of the felt's thickness. Finishing the cervixes involves hand sewing and a lighter felt, where the stitches are still visible, is easier to work with. This is best achieved by hand fulling.
Run the knitted piece under hot water. Use a mild soap, such as castile or olive oil. Rub and agitate like you're trying to get a stain out. You can also use a washboard for this stage. After a while, alternate between hot and cold water to "shock" wool. Repeat. You will start to feel the piece firm up and the stitches will become less distinct. Allow to dry, turning inside out to make sure both sides dries thoroughly.
Fold bound off edge in half, thread tapestry needle with tail and sew facing edges together. Stuff with roving or polyfill and sew cast on edge - make sure the seams are aligned. Do not cut yarn. Sew through the center of cervix from cast on seam to bound off seam, sew across, pulling tight to create an indented line. Bury tail in center. If you want, you can embroider along the seam with darker pink yarn.