u/Gold_C0mplex

For context I am a complete beginner. I have no idea how or when this happened, but when I went to texture my object I noticed some Z fighting on some of the surfaces. I thought it was a render issue at first so I tweaked some settings, but then I tried moving some faces and to my horror there were duplicate faces clipping through the originals. I have no idea how this happened, but if I had to guess it was probably something to do with the mirror and solidify modifiers I was using earlier in the process. Is there any easy way to fix this or am I better off just starting over? Any tips to avoid this sort of thing in the future?