I stepped on a rusty nail last tetanus shot was 3-4 years ago should I worry. Should I be worried?

Not about tetanus. Your tetanus coverage should be fine. There are many other germs I would worry more about and an infection into the complex structures of the foot can be scary. Make sure the wound is thoroughly cleaned and examine it frequently over the next few days. Go in if there is increasing redness/swelling or pain.
See below. As far as your tetanus status, you are good. However, watch for signs of a skin infection, redness, swelling, warmth, and mucous discharge.