you didn't get tetanus from that.
if you live in the US then you did, indeed, have several tetanus shots growing up. it will have been in the dpt shot (it has other acronyms as well). My 13yr old just had her booster this year. I am trying to remember if my son had at booster at 18. He may have. tetanus boosters are good for 10yrs. My last tetanus shot was 3/2006. so in a 1 1/2yr, I will have my doc hit me again.
the likelihood of you contracting it, ever, is pretty small. I do a LOT outdoors. so for me, it makes sense. Personally, I think it makes sense for everyone.