Urgent help needed for jam recipe!

[Daisypod]

I'm hoping someone can help at this late hour!
Last autumn I picked loads of blackberries to make jam, I hadn't got round to it yet and they've been in the freezer. On Thursday it defrosted so I needed to use them asap.
I got preserving sugar and jars finally and tonight I've been making the jam. It's not doing the thickening on a frozen plate like it's supposed to! I've been boiling it for about 30 mins.
I've just read online that preserving sugar doesn't have pectin in and I should have used jam sugar ( I did add lemon juice as the recipe suggested)
Is there anything I can do? It's still on the hob now. There's absolutely loads and I'll be gutted if I've ruined it all.

Do you have any apples you could cut up and chuck in for the pectin?

Yes! Thank you, off to do that now

I'd turn the hob off now. Buy some pectin tomorrow and retry it with the pectin.

Good luck!

@AlisonDonut I've already put the apples in now so I'll give that a bit of time and if no luck I'll try what you suggest, do you think that will be ok?

Do you have a jam thermometer or anything you can use to measure the temp? I make quince and crabapple jelly and I never could get that dratted plate thing to work properly, the thermometer just tells you if it’s right or not.

It will be ok if you just leave it overnight and try again in the morning though, if you get stuck. Try putting one lot in a small jar or a little tub and see if it’s set in the morning when it’s cooled down! and I agree apples will help with pectin.

If it doesn't set it's not the end of the world and it will still taste miles better than jam from the shop. Just don't wear a white top when you eat it.

My jams sometimes don't set, but like @BlackForestCake says they're still delicious

Thank you for all the help. I've ordered liquid pectin and it will arrive today so hopefully that will do the job

If you don't have pectin you can always use one of these substitutes.

superbsalt.com/pectin-substitute/