The problem with the recipes that use commercial pectin products is that they often take no account of the water or sugar content of the fruit, or of the amount of heat you are putting into the pan, because they tend to say things like, "boil for 4 minutes". Be aware that bubbles can start to rise in the jam before it gets anywhere near to 100 degrees C, so you think its boiling when it's not if you don't have a thermometer. They also use more sugar than conventional jam recipes, and this can cause the jam to become too hot too quickly.
You can try to re-cook it. Put the jam into a pan with around 100 ml of redcurrant or lemon juice, and stirring, bring it to the boil. If you have a jam thermometer, you want to reach 105 degrees C, but you may reach this too quickly because of the amount of sugar in the mix. So, once this jam is boiling, reduce the heat slightly to maintain the amount of heat going in rather than make the jam hotter.
Stir slowly and continuously. The object will be to reduce the water content of your runny jam, and at the same time get it to the right temperature.
From time to time, reduce the heat right down and stir, you will see the steam being driven off.
Hopefully, after about 10 minutes of this, signs of setting willl be evident.
You will see and feel (as you stir) the jam thicken and the bubbles change to give a more plopping sort of a sound. The jam will form more of a sheet than a drip when you drip some from a cool ladle. and it will have a jagged edge when it separates. The final drip/sheet will hang from the ladle. Have a plate already chilled in the fridge. drip some jam from your lade onto a teaspoon, then put this on the plate and pop it back in the fridge for 5 minutes. Take your jam off the heat when you are waiting. this blob of jam will wrinkle if you push it. if you draw your finger through it on the plate, you will see that the line you formed stays intact.
These signs of setting are hard to visualise until you've experienced them, but give it a go, and best of luck!
