It may not have been you that killed them. Maybe I gave you seeds that don't do well in your area. It's hard to say without being there to see.
If you have cosmos coming you should have some for next year. Mine are about a foot or so now. Coming along.
Coreopsis can be tricky to grow. It needs the right spot or it just won't do a thing.
Umm, my gardens really aren't great right now. I am just getting really good at cropping pics.