whenever i extrude a loop, it mangles it. I have all the usual stuff applied to the retopology plane (snap to surface, mirror, subsurf, and shrinkwrap). this problem doesnt seem to exist in any video ive watched on retopology. any idea whats going on?
Generally I don’t do retopology by doing entire loops very often, but if I do, I do it in vertex mode. Looks like the verts are snapping to the surface in a strange way, including each other. In some cases, depending on the scale of the model, back side surfaces are selected. Looking at it again, it looks like you selected the entire loop and then tried to move it. Things will snap to the surface that you are looking at, so the verts on the other side are being pulled to the surface you are viewing and mangling the mesh. Blender does a good job at retopology, but other tools (software) that specialize in it usually keep things in order better. It can be a pain, but focus only on the side you can see.
turning snapping off while in edit mode fixed my problem, and the loops were duplicated with no errors.