No, that time frame was more then fine to detect a syphilis infection. Also you were treated so even if on some very very very rare chance it was a false negative it would have cured the syphilis.
What else could cause a rash on my palm and foot? It seems so conincental
Rash could be so many things, would have to see a DR.
the rash might be a simple case of eczema. I would make sure the dr you see or saw is a dermatologist. If it's eczema, a topical steroid will do the trick to resolve. But it sounds like you are definitely clear of syphilis, especially having gotten the penicillin shot.