I used an old box of Sure-Gel. I mean, it wasn't SUPER old... Maybe 2 yrs max? I'm wondering if the fact it was old contributed to the fail? I was uber careful with the measurements to make sure I didn't have anything over or under the recommendation.My opinion, you wanted jelly, so make it into jelly. I found this Ball pectin calculator that might help.
https://www.ballmasonjars.com/pectin-calculator.html