17 p injections

Meredith
Hi, I have been taking 17p injections since 16 wks. Went to the dr and have been having contractions...currently 1 cm dilated. This is the first time I've ever dilated this early! and the first time I've ever taken the 17p. Does anyone have any experience with this shot? My dr told me it helped to
Prevent preterm labor...doesn't seem to be working for me and I'm scared!