When is the last time you had a tetanus shot? I was told you should have one every 10 years. Did you clean it well? I stepped on a rusty nail once and I cleaned it with soap and water, as well as soaked it in salt water(a little salt) for 15 minute every day for three days. If it doesn't look infected you should be ok. If you see any sign of more then a little redness you should see a doctor. Good Luck.
If you are unsure when you last had your tetanus booster, it would be a good idea to go to the ER to get a booster shot.
It is not worth taking the risk.