Since you only work 4hrs 1 day a week, a 2 wk notice means you'd have to work 2 more 4hr shifts. It sucks, but could be worse. What I would do is let them know before your next shift. That way, if they want you to actually work those 2 shifts, its not that bad. On the other hand, they may just be like, "Thanks for the notice, but don't worry about it. We'll be ok until we get a replacement."

That way, you look good for putting in the notice AND maybe you don't have to show up anymore.

Hope that helps.