Entire sequence has shifted to the left?

I have absolutely no idea what I did but I'm in crunch mode for a video and I noticed a little bit ago that, when I put in a piece of text & clicked the Essential Graphics button to center it, it wouldn't center - it'd be a little to the left. I've noticed now that everything in my sequence - clips, text, images, etc - has shifted about forty points to the left, completely reframing every shot, cutting text out, etc. In the Effect Controls on each clip, however, the Position values are at their default (960, 540). I've gone too far past this into my sequence to undo it. Does anybody have any idea what I did or how to fix it?