Hi Mala, how are you constructing this surface exactly? The file size has grown large because the surface is extremely dense with a huge number of control points in it.

For filleting, if you hide your curves you should be able to see that there is not any edge in the area you want to fillet, the surface is smooth there although it goes through a very tightly curved bend:





You'll probably need to build this in a some separate pieces instead of all in one single sweep.

- Michael