I broke my Jam.

Please don't laugh - The kitchen and most thing in it are a complete mystery to me, its all black magic I tell you.

I tried to produce some Jam yesterday with the huge amount of yellow plums I have. I made 2 batches the first I followed a recipe using 3lbs of fruit and 1 ½ lbs of sugar. It has set but is  so sweet it is almost inedible (at least for me).  The second batch I used 3 lbs of fruit and 1lb of sugar and its not set at all and is still a little on the sweet side.

Can I fix the second batch ? I don't want to add more sugar though - A quick Google showed pectin available in sachets, can I reheat the jam and add some? Will it set properly or just taste rank.

I've got a tree full of damson to use soon so I was hoping to get  it right before then.

On a side note - how long will the burns on my arms take to heal where it spat at me 

Yes you can re-heat it and add pectin. Silver Spoon Pectin is available at Morrisons and Asda (plus some Co-ops) and comes in a packet with 3 sachets for £1.25. You should only need 1 sachet if you've used 3 lbs fruit to 1 lb sugar. Do remember to thoroughly clean and re-sterilize the jars before you put the jam back in and discard any discs that you may have used.

Also adding lemon juice helps cut the oversweetness, my OH hates very sweet stuff so I'm always having to adjust the sweetness.

That's smart idea