Agreed, you hit a nerve with the needle or some of the oil is pressing on one. Even if you can't fully flex, the fact that you can use the muscle, that means is funtional, which means the nerve damage is temporary.
In case it's just oil pressing on the nerve, massage the muscle as much as you can so it speeds up the dissipation.
I had the same thing happen in my outer quad with a prop injection. I wasn't able to flex my outer right quad for a year. Biceps though are much smaller muscles and they recover much quicker.