What do I do if my turkey is done way too early?
If possible I'd remove it from the oven and slice it up and put it in the fridge to cool it down as fast as possible to stop the cooking.

When closer to serving, just reheat the meat.

You can pour some of the juice on the carved slices to keep them as moist as possible.

For christmas, this is what we will do (more "extreme) and cook the turkey one day in advance.