Wrong kind of steroid. Absolutely do not do this again
You are thinking of corticosteroids. Testosterone is an androgen. The nomenclature "steroid" in common speak is confusing; the only thing they share in common is that they are hormones our body produces. Get corticosteroids if you need them.
Shooting into joints or tendons is terribly dangerous for non med-professionals. Shooting oil anywhere but the muscle or subQ is dangerous. 10000x as true if you are getting your T other than straight from Walgreens. This is coming from a guy who's shot heroin and coke in his finger/foot veins: seriously, don't do that.
If this worked once, bow down and thank your local deity, because you won the lottery. You could've lost use of an arm.