Hi, I'm just curious if there's a way to either remove, or decrease the size of the circle of the sketch tool. Not the size of the actual tool and drawing, but the annoying huge circle around it, which makes it very difficult to gauge my lines.

You probably have set the stroke smoothing on the Tool Options Docker to "stabilizer"
Either uncheck the "distance" checkbox or change the stroke smoothing mode to something else.

Unfortunately, that doesn't seem to be the issue. The tool itself just has a large, necessary circle around it, even without smoothing/stabilizer options checkd.

Or do u mean preview outline ?
Setting > General > Outline Shape > No Outline

If not , you can show with Screenshot so others can help you

The sketch brush engine's brush outline signifies the area which the sketch brush takes into account when calculating the sketchy effect. The only way to disable that is to disable globally the brush outline, like gui-m suggests.