Half of the skill of jam making, is knowing when your jam has reached the Setting Point.
Take it off the heat to soon, and you will be left with compote. Leave it on too long, and it will be unspreadable!
Here’s how to tell when your jam has reached that ‘magic moment’:
Don’t panic if it doesn’t set. I had this issue before, and can report back that you can ‘re-boil’ your jam, and have another go!