It looks like you might have used epoxy intended as an adhesive, and probably the quick-drying sort. you would be better off with a resin made for pouring, casting or imbedding. Here is something close to the full story on epoxies:
Epoxy - Wikipedia, the free encyclopedia
Epoxy does cure quite progressively, and there is a stage at which, if anything is going wrong, it can easily be scraped or pared away without damaging the wood.