Unfortunately adding steel-cut oats to an extract kit (I assume this is since you have steeping grains?) is going to just leave you with a starchy, hazy mess. Oats need to be converted, which means you'll need to mash them with some base malt. Not a big deal, it can be done as a partial mash with some 2- or 6-row malt. Easiest to do with instant or rolled oats, since they're pre-cooked, but you'll have to gelatinize the starch (ie, cook) in the raw oats before they can be extracted from the grain.