If you prefer not to use powdered pectin, you can always add some granny smith apple to the batch, it won't change the flavor, and green apples have a lot of natural pectin. This would also help keep it tart, I'm not sure how much apple, but I've heard it works. The apple will cook down and disappear.
I had the same thing happen to about 8 qts of strawberry jam, my old Kerr book said to add sugar and low boil for 20 minutes. It got quite a bit firmer, about medium-firm I would guess. Was not runny at all.
If you ever get the choice to sit it out or dance, I HOPE YOU DANCE.