Pinch in my back from bad form???

Yesterday I worked on shoulders and did 3 sets of '
Standing Dumbbell Straight-Arm Front Delt Raises' The first two sets were tough but i got through them, the last set I pushed through but I noticed I had to use my core a bit more to the point of almost pushing my belly out. Now I have a bit of a pinch in my back. Is this due to poor form? Should I have stopped with less reps?