This is happening because platinum is a soft, easy to scratch metal.
The reason that old-time platinum rings lasted so well is that they
were die struck under tremendous pressure which hardened the metal,
and they also did not feature large shiny sections. Instead, they
were covered with hand-chased ornamentation that disguised scratches.
Your ring was probably cast from the easiest to cast platinum alloy,
giving you a lump of soft metal instead of an heirloom quality
keepsake. Sorry for the bad news.