I recently injured myself by slapping a mirror. i tried to remove as much of the glass in my hand as possible but it still feels like there some left.

Time, patience: Small pieces of glass often extrude by themselves over time. If they can be seen or felt externally, they may be removed like a splinter. If they are deep or can't be felt externally, they are extremely difficult to find surgically.

See a doctor: An xray may show where the remaining pieces are. You don't want to root around yourself and cut something important.