I am in the middle of making Merissa's Raspberry Filling, which is
delish and ran out of corn starch Is there anything I can use as a substitute. Cake is due tomorrow

For 1 tablespoon cornstarch, substitute 2 tablespoons all-purpose flour;
or
1 tablespoon potato flour or rice flour
or
4 teaspoons quick-cooking tapioca;
or
2 teaspoons arrowroot.