You could try this:
- create another single-face sheetbody by extruding a profile (of the edges) with distance 0.
- xform it a little in the right direciton
- refit the new body towards the original multiface sheetbody
I think it is no good idea to try making a single face. You have a combination of planar faces with two cones and freeform faces. Putting them all together will lead to a complex free form surface, and you'll not fit the shart edge of the two planar faces.
The problem with offsetting seems to be a result of tangency failures between the single faces.
I suggest to model the cones and the planar faces and in a second step the outer faces as a single one which is tangency to the others.
You colud create a very simple bounded plane with the circle and the oval inner shape and then use the refit command to deform it.
Production: NX10.0.3, TC 10.1.4
I was simply answering the question on how to make a single face. And yes, it would be within a tolerance.
If the problem is making an offset, then I need to have the part. The topic is asking two questions, but we can only answer one of them.
Rough Offset is also a nice feature if this is about creating an offset. (I must admit I did not read carefully and overlooked the offset questions because of the CAPITALS).
I think that it is important to note that even if you do rebuild this as a single sheet, it may not solve the offset issue. If the end goal is an offset of this shape, try the "offset surface" and "rough offset" commands first; both have some options to exclude or heal problematic areas.