Need Help with surfaces

i am new to rhino and a have problems with surfaces in rhino, when making a patch surface the surface does not fallow the curve,
thanks in advance

You are seeing the effects of meshing surfaces. To be able to render a surface, Rhino creates a mesh that is based on the settings in the document settings. You can change these to make the mesh denser and have it more closely follow the curve.

Further reading:

Thanks for the reply
the problems affects the vray renders renders too.
i resolved the problem by going to File > Properties > Mesh or Tools > custom and setting density to 1