>>1888441If you use the magic lasso, make sure to Grow your selection a bit before doing Color to Alpha. You might also want to Feather the selection, depending on the image.
But the best renders are done without (only) relying on the lasso. You have to go over the image with the Brush tool in Color Erase mode, making sure to keep the edge of the circle inside the outlines.
And make sure to add a layer under what you're working on that's either black or some other color that will make issues obvious (I sometimes use an obnoxious bright green).