Hi,
your filter is mismatched meaning that resonators are not on the right frequencies. You can tell this by examining the reflections - you don't have distinct dips in response. Regarding this, even your simulation doesn't look 100% OK - reflection dips for this class of filter should be symmetric in the passband. One reason for discrepacy between simulation and measurement might be that you did't include step discontinuity in your schematic. After this you should retune to achieve desired response. As a final check do EM simulations
flyhigh