Does this diagram look right? A level physics help

You've got the general shape right, although in reality there would not be such a sharp change in direction between the diffracted wave fronts and the ones moving straight ahead (it would be a more gradual curve).
A useful trick you can use here is to image each wave front being broken down into a line of point emitters (this is known as Huygens' construction) and then seeing that the ones near the edges of the slit are partially blocked, and so the total wave front when all the emitters constructively interfere is bend through an angle in that area.