Just bought a 52mm hood, but it doesn't fit...

The hood you buy needs to be the same as the inner ring on your lens. If you look at the inside of the lens ring or on the outside of the lens it will tell you what size filters will fit your lens. If the 52mm is too small or too big you should be able to find a adapter for it so it will fit. Try going to B&H photo website. They have tons of photography items. Hope this helps.