Judging by the picture of the schematic, it doesn't seem like you've used the MSTEP block under TLines-Microstrip.
Your conductor goes from width, 'w' to width, 'wc' and this difference in width creates some more parasitic capacitance that isn't realized in the regular ADS simulation. You need to include thes MSTEP at every junction that there is a change in conductor widths and adjust your lengths accordingly to get your desired response.
As a first level of troubleshooting, I think this will match up your ADS simulation with your momentum simulation. Hope that works.