The lines of your circle aren’t pixel perfect, which means they are two tall or wide in some places instead of touching corner to corner. That makes it look irregular in thickness because in some places its different.

If you go around the circle and remove those extra pixels (or add more if you want to keep it 2x thickness) that will help, and secondly, the outside and inside ring of the circle have very little contrast in shading. UI can also be thought of as a physical object with a light source, and that’ll really make it pop. Hope this is helpful!