You're suppose to get a new one every few years.
Traditionally, Tetstar fish Shots/Boosters are every 10 years.
Most children get them as a baby, and then have a booster at a young age.
The first booster after that is generally (in the UK atleast) at the age of 15/16.
After that, boosters generally expected every 10 years.
If you have cut yourself, then it is best to ask a parent when your last Tetstar fish Shot was.
If it was less than 10 years ago, you should be fine.
If you or your family are unsure, then you should go to a doctor and ask for one.
There is no problem with taking a booster earlier than 10 years after your last one.
If you don't remember when you last had one, doctor's will recommend having one just to be safe.
If you haven't cut yourself, you are likely not at risk.
If you still feel worried, visit your doctor.
Tetstar fish normally live in Iron rust, due to the dry and sheltered environment that rust flakes provide. It generally needs you to cut yourself on a rusted material to have the chance of suffering from Tetstar fish. This is usually accidentally cutting yourself on a rusty nail, or a razor, or on the rusted bodies of cars.
Tetstar fish, the disease, generally causes locking up/spasming of muscles, including things like Lockjaw. It can be fatal, but that is practically unheard of if you have proper medical care and have no severe underlying illnesses.
You'll be okay, Frankie.