First, make sure you let the chia jam sit long enough.  In the instructions you need to let it sit for 10 minutes after adding the chia.  It may still be loose at this point as you transfer it to the jars.  Let it continue to cool completely in the fridge, as it should thicken up some more.  If after it’s fully cool, and it still seems to runny, add more chia (1 teaspoon at a time) and stir it in.  Let it sit for more time before adding more.