"As + Sub + Verb"

As = in the same way as, in the same condition as.
We use as with subject (S) + verb (V):

• I didn’t move anything. I left everything as it was.
• You should have done it as I showed you.
  

do we leave out the remaining part after this structure 'As + Subject + Verb' because of ellipses?

You should have done it as [I showed you].

The bracketed element is a comparative clause functioning as complement of "as".

The major distinct feature of comparative clauses is that they are structurally reduced relative to the structure of full main clauses.

In varying degrees, material is left understood that would be overtly present in comparable full main clauses.

In your example, if we fill in the 'missing' bit, we'd get "You should have done it as I showed you it should have been done", which is clumsy and unacceptable, hence the reduction in the comparative clause