Dilute the with copious amounts of mineral spirits of some other effective solvent using a cotton ball, and pull out the stain after it loosens (while still wet) by carefully dabbing with dry terry cloth. This may take 2 or three applications of solvent. The stains will not be totally gone, but the sail will look weathered. Stains on sails are normal and if diluted and subtle, can add realism. The idea is to remove as much as possible. You just don't want too much contrast, such as happened with your accident. At least it doesn't look like this:
HMS Victory's fore topsail, removed after the battle of Trafalger
Question: What does the front of your shirt look like?