If you get some lemon or orange pips and boil them up they are stuffed with pectin. SO maybe - store jam, covered in fridge preferably, eat lots of oranges or lemons or grapefruit, store pips. Then give them a good boil, notice that lots of goopy stuff comes out, strain, used goopy pectin loaded liquid and throw pips away and then re do jam. Bit of a faff it's true and a packet of pectin would be a damn sight easier. I found out about the pips while experimenting with marmalade.
Apple pips and woody bits probably work as well.
Early for strawberry jam? - oh , no its not, the weather is creating an illusion that it is still April.