Sauerkraut soaks up too much liquid while fermenting I've been fermenting sauerkraut in a quart jar and for some reason forgot to keep an outer piece of cabbage to help keep the kraut submerged. For day 1-2 it was fine, there was plenty of brine to keep it submerged. Now though on day 3 and 4 the brine has all been reabsorbed into the kraut and no matter how much I push it down, in a few hours it's exposed again. Do I still need to worry about mold at this stage or has 2 or 3 days fermentation been enough to preserve it? Or should I top off with a brine solution or would this just add unnecessary salt to what should be now a pickled flavour?
It will likely mold on top, where the cabbage is exposed.  You can simply remove that layer, the kraut below will be fine.  Alternately, you can top it off with brine...or use a container, smaller than the opening of your jar, filled with water, to weigh it down.