Cone shells can be poisonous, but the cones found in Fl are not. The alphabet cone, as Wini mentioned, can discharge a pretty hurtful sting, but finding a live one is rare. That said, I have found a live one, and just quickly and gently put it back down.
Dont' worry Annesurfs, those pesky pen shells are the worst thing you'll encounter on the beach. I'm so glad you're coming back!! Did you ever get your shell mirror?