Overnight oatmeal still underwater?
The instructions on www.mymccanns.com that I can find read:

Quick Soak Method
One of the quickest and easiest ways to prepare McCann’s® Steel Cut Irish Oats is to soak the oats overnight. Before going to bed, boil 4 cups of water in a pot. Then add one cup of oats and simmer for 1 minute. Cover the pot, cool, and store overnight in the refrigerator. The next morning reheat over low heat, stirring occasionally.

Although these are instructions for overnight soaking, they aren’t instructions for ‘overnight oats’ that are popular to eat cold. Was that what you were aiming for? I read this as a process to reduce the 30 minute cooking time they suggest for ‘Irish porridge’ further down the page. As you can see the final sentence tells you reheat the oats next morning. Presumably at that stage the oats will swell and thicken the remaining liquid to form porridge.
If these are the instructions you were following, they will not yield ‘overnight oats’. I think you really need rolled oats for that.