Are you using fine silver, or Sterling? Either way, I suspect that
your piece is fully annealed and thus very soft. One thing you could
do is tumble it in stainless steel shot for a while, which will
harden the surface nicely.
Freshly cast silver ingots, which I work with fairly often, are
extremely soft, and you can mark the surface with a fingernail. After
working, the silver becomes much harder.