Mirror got glitched in sclupting

I added two back feet to my sculpt from a separate file that was appended then joined them using ctrl j, and now the mirror is all messed up and completely off balance. I’ve done this sculpt 100 times trying to get it right and this kind of stuff keeps happening near the end and ruining all my projects please help. here’s some images to show you what I mean

Hi. It looks like the Origin was moved. Did you join TO appended object instead of main?
Try Object > Apply > All Transforms to set origin point to World Origin.