You didn’t do anything wrong and yes, your jam is safe to eat. Sometimes condensation happens, but you don’t need to worry about it because the water in the jar has been sterilized during the water bath. Therefore, the water will not cause mold or bacteria to grow in the jar.
On another note, it is always a good practice to examine a sealed jar when you take it off the shelf to eat.
First, be sure that you “pop a seal.” A jar that was safely sealed a few months ago could possibly lose its seal on the shelf, although this rarely happens. Then look for identifiable fuzzy mold, a moldy smell, or a fermented (alcoholic) smell. If any of these are present, throw the contents of the jar away. It’s not a good idea to eat moldy jam or scrape the mold off and eat what’s below it.
An open jar of low-sweetener jam or jelly can be expected to last about 3 weeks in the refrigerator.
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Posted in: 6. Questions About Jam-Making Equipment and Water Bath Canning, 7. Troubleshooting