Hi Olga, if you have the 3DM model file if you could post that as well it would probably help to see how it was constructed.

But it looks like the shape there is trimmed from a larger smooth surface.

It can often be easier to make a smooth shape if you make a larger extended surface and then cut it.

I think that one of Jesse Kaufman's tutorials is similar to what you are looking for there:

http://moi3d.com/forum/index.php?webtag=MOI&msg=510.5

- Michael