There are so many aspects to knife making it's difficult to diagnose the problem over the internet.
When I was doing full tang knives, I had to be careful of numerous things.
Make sure the handle pieces and tang are DEAD FLAT! Make sure they are roughed up so the advesive has something to "bite" to. Drill holes completely through the tang and just partly through the handle material. Clean with acetone or denatured alcohol before attaching.
Don't clamp so tightly that you squeeze out all of the adhesive. I would place little tiny pieces of tape here and there so that no matter how tight I may have over-clapmed it, some of the adhesive would remain for sure!
Don't depend on adhesive alone - you shold at least place a few pins or bolts in the handle material on a full tang knife.
It's pretty easy to do an internet search for knife making tutorials to get step by step instructions.
Hope something here may have helped you.