Can the shot to stop early labor not work?

I'm 34 weeks and 4 days and went in for contractions. I tested negative for early labor so they just gave me the shot to stop contracting and it worked for an hour until I wasn't jittery anymore and started again once I got home. My hospital is 30 min away and I don't want to go back now. What do I do? Is it possible the shot didn't work?

This is my second baby and also a back to back pregnancy