Every year I buy a bottle of Laird's and make Jack Roses around the winter break. And I'm...doing that. Applejack isn't that easy to find, a lot of liquor stores don't bother to carry it but I found some.
I made the grenadine a little too thick this year, it's a proper pancake goo rather than a sugary liquid but it's still tasty. I think next year I'm going to buy fresh pomegranates and milk them myself rather than buying juice.
How did you make it to thick? If you boiled off water, you should just be able to add water back to it. If you made it too sugary, you should just be able to leave it out of the fridge.
There's another possibility: it hit a boil I couldn't stir down, which is similar to a step in jelly making. It's not impossible I activated some pectin in the juice and thus it has partially jelled.
But, it's more likely that I boiled the 2:1 syrup a bit too long/hard and diluting it would help. But, you know what? It shakes up into a decent cocktail so I'm just gonna deal with it being a little thick for a few days. If licking fruit syrup off a spoon is the worst I've done to myself I think I might get by.