What are the chances of someone getting rabies from getting scratched(broke skin) by a metal piece that was possibly wet on the ground in my house?

None. : Rabies is a virus which is transmitted from infected animals, usually but not only, dogs - by bites or licking of wounds. So u cannot get that from a metal piece in ur garden. You may be thinking of Tetanus which is more likely in the scenario u described and u shd make sure you are up to date with your tetanus shots which in adults is once every ten years.

Wash it well: Wash it out aggressively. Then get your tetanus shot up to date if you haven't had one in 5 years or more.