If you can provide documentation (primarily for the illness), look into whether you can appeal for a retroactive withdrawal from your Chem class by talking to a dean or advisor. Sometimes universities do the right thing.
Secondary essays often provide an opportunity to explain a blip in your academic road.
You may need to wait until after senior year or after a fifth year to apply in order to get your GPA into a more competitive range. But no matter what, "making the mess right" starts with getting near-straight As from now on.