Tinker123

This is a very basic question, but I have created a drawing using the vector brush tool. Some of the lines got sloppy and I want to erase bits here and there. When I attempt to use the Eraser, it causing pixillation around the edges, instead of a nice, smooth erase. I'm sure there is a setting I can change, but I've looked everywhere and can't figure it out. Can anybody offer some assistance? I've attached a screen shot of what I'm talking about. Thanks in advance