Will I get tetanus from this rusted metal scratch?

Maybe,maybe not. Any wound that opens the skin can allow tetanus spores to enter and create an infection.Those germs produce the toxins that cause tetanus. A rusty nail is a classic exposure.If you had a booster within 10 years & cleaned up the wound after receiving it, you are likely immune.If you can't remember receiving a booster within the past 10 years it is a good idea to get one.
Booster needed. If you have had a tetanus shot within the last ten years, the chances are remote. If you haven't had a booster get one now.