Shouldn't have told Lydia it was ricin. Now she has a chance to tell the docs exactly what's wrong with her, unless Walt waited to tell her after it was too late.
Jesse's prints are all over that place, and the gun. He could still get busted but we'll never know. Walt tied things up as best he could.
Only takes ~40mg of ricin to kill a person if it is ingested. Sugar packets contain ~4000mg of sugar, so yeah...