You need to put a tear away stabilizer in your embroidery hoop.
Then keeping the 505 spray or temporary spray of your choice away from your machine spray the stabilizer. Mark your towel as to where you want your embroidery, your book should help you with placement, then stick your towel on the stabilizer with the hoop on your machine. Then spray a piece of plastic looking stabilizer on top of the towel to keep the stitches from sinking into the towel. Be sure the plastic type stabilizer is wash away.
After embroidering the tear away will come off the back and the plastic will tear away or wash away. Hope this helps.