In my schoolyard scale electric J-3 Cub plans it states "Contour sand the leading edge using the contour gauge provided. If left with sharp edge wing will stall."

A] I have a simple, if not ignorant, question: What is 'wing stall'?

B] Also I made the mistake of gluing the left panel wing tip flush with the tip rib bottom (flat on the building board) instead of off-center with the rib and centered with the leading edge. I filled the gaps nicely at the leading and trailing edge with scrap balsa but would like to know: I know I will have to do the same with the right wing panel but . . . will the slight displacement of the tips cause any significant difference in the flight or the tip's airfoil characteristics?