I tried making jam for the first time. Since I have a hard time following recipes I used David Lebovitz no recipe cherry jam recipe. I used 5 pounds cherries (weighed before pitting), about 2.5 cups sugar, and the zest/juice of two lemons. When I did the plate test it just got cold rather than setting. So my question is how do I fix it. I don't want to add more sugar. Can I but a pectin product, reheat the jam, and add the pectin?
P.S. My intention was to do freezer jam since again I can't seem to follow recipes.