Yes indeed!
As you can see in layout, there is no side ground created. Layout just draws a zero width line to indicate where side ground edge starts. The second issue is that not only the side ground is missing, the ground pins are missing as well. So your simulated structure is a microstrip line, with ground return at the bottom of the substrate.
You can use my application note on parameterized layout for EM in ADS:
Your RF EDA solution partner since 1993
muehlhaus.com
but CPW is a bit tricky.
If you do NOT need to include metal thickness, and zero width EM solution is good enough, you can use the lot mode in Momentum where you draw the SLOT instead of the conductor. Then you could use (abuse) the MCLIN microstrip model to generate the layout (representing the CPW slot!).
There should be some instructions in ADS online help on CPW simulation using the slot mode.
Good luck!
Volker