This is my first time making perserves. I got the recipe from Cooking Light Magazine and I am afriad I left it on too long. They are sticking to the top of the jar from when I turned them over to cool. When I opened a jar they are still sticking and it is hard. The recipe called to leave the ingredents for 12 hours covered. Then bring back to a boil and simmer for 1 hour and 15 mins or until thick. What is thick? Just thicker than normal or the whole pan should be think? I am not sure how to tell when to take it off then stove. Thank you for any help.