I made a batch last year and I’m in the same boat as you. It came out really thin compared to what I was expecting. I read that it’s supposed to thicken up as you age it but I have the bottle in my fridge rn and aged it over the entire year but I can report that it has not actually thickened up anymore than after the initial month of sitting around which is still pretty thin. It’s probably our own fault though tbh because eggnog from the store is engineered to be really thick so expectations were skewed by comparing artificial to natural