Don't know what recipe you used ... no added pectin, added liquid pectin, or added powdered pectin. The "fix" depends on that.
Making jam is really not a mystical art which only a few can master ... it certainly doesn't have to be a case of "Double, double toil and trouble; Fire burn, and caldron bubble. Cool it with a baboon's blood, Then the charm is firm and good." (Macbeth) If you're using added pectin - you follow the instructions for the pectin you are using ... if without added pectin you have to cook it to the gelling stage ... the times and temps are only guidelines - sometimes it talkes a little longer to get a gel based on the pectin content of your fruit. I use a triple-test method ... once the pot is up to temp I start using the the spoon test, and when that looks good, I then use the freezer test to confirm it: Testing Jelly without Added Pectin
Now, to fix your runny jam .... you might try this: Remaking Soft Jellies
While I will agree that the Ball Blue Book of Home Food Preservation
used to be the defacto primer every canner should own ... these days you can find all of the relevent information at the: National Center for Home Food Preservation
. And they have a good section on: Making Jams and Jellies
Hope this helps ...