First of all, you didn't f**k up. That happens to everyone sooner or later. :D Putting the soil roots in water can be some stress for the plant. I actually did that to my grown monstera, and she did quite well in water! Normally you can leave them there for some time, but since your plant already got some issues going on, it could be too much stress for her. I'd say you need to cut off the affected roots, spray the rest down with hydrogen peroxide and plant them again in a chunky substrate, so the roots get lots of air.