I’m fairly new to texture painting so please bear with me. I want to paint a simple texture onto an object, but every time I paint, the paint mirrors onto the opposite sides twice! I don't have “Symmetry” enabled (pic 1) so that it won’t mirror like this (GIF). But it still is. Why is my paint mirroring? If I paint just the UV, it doesn’t do this, but I really want to paint the object. My TVs are in pic 3.
Your UVs are extending the bounds of the image texture or more correct of the UV map, which always ranges from the bottom left of the texture to the top right. Which means, Blender does not have individual image data for those parts of the mesh, so they are filled according to whatever extrapolation mode is set in the Image Texture.
By default this setting is Repeat. This results in the image texture being repeated across its bounds like if you would have tiles of the image texture. The UVs lying outside the bounds get those parts of the image according to their position on these tiles:
Another setting would be Extend. In this case the pixels on the top, bottom, left and right border are extended in their respective directions so they get stretched over the UVs that lie outside the bounds:
The setting Clip does not repeat images or pixels outside the bounds - it just leaves an empty i.e. black space for UVs outside of the UV map bounds, this can be helpful for something like decals etc. which should only appear once on an object and definitely not repeat but be mixed with repetitive tiling textures:
And last but not least the Mirror extrapolation. It is repeating the texture as well outside the map bounds, but always mirrored on the border:
Most likely your setting is Repeat, because it is the default. But in your case it will not help you if you change the extrapolation mode, because you probably want all parts of the mesh painted exclusively without repetition. So you need to place the UVs of all faces inside the bounds of the UV map / image texture to paint them all individually and nothing gets repeated. Also from what I see it looks like some of the painted parts are stretched, so maybe a new UV unwrap would be good which keeps the aspect ratios of the faces consistent.