In my experience, either the anchors are fit for the job and the wall, then 1/8 doesn't really matter (especially like in your case, when it's not somewhere by itself, but in a line), or they are completely useless, but then even the 8 wouldn't do it.

The cleanest procedure would be to take the shelf down again, take our the spinning screw, take out (drill out) the anchor, still a new, slightly bigger, hole, or in New, sorry bigger anchor, put in slightly bigger screw.

I seldom bother with cleanest procedure xD