Roberta,
There are many reasons why your resin isn’t curing. The two big things that I would suggest you start with are that you are
1. Measuring accurately
and
2. Mixing thoroughly
I would say these account for approximately 75 percent of curing problems that I help people with. Beyond that, its almost case by case dependent. Heres a link on our blog with some other troubleshooting articles: https://www.resinobsession.com/tag/troubleshooting/