My painted board has 2 coats of shellac & has dried for 2 days. But when I place a piece of décor on it, it leaves a mark.
Shellac applied in thin coats normally dries very quickly, but it won't harden completely if the shellac is too old. Check the can -- there may be an expiration date that'll help you judge how old it is. If the shellac has been stored in a warm place, like a hot garage, that can shorten its useful lifetime.
You can check the condition of your shellac by spreading a bit on a piece of glass. The shellac should harden quickly; if it doesn't, and instead remains tacky or gummy, then the shellac is too old.
I'd let the piece sit for a while longer if you can -- maybe you'll get lucky and the finish will fully harden with more time. But if it seems like it's never going to harden, then you can remove the shellac with alcohol.